Branched amides of L-aspartyl-D-amino acid dipeptides

ABSTRACT

Amides of L-aspartyl-D-amino acid dipeptides of the formula ##STR1## and physiologically acceptable cationic and acid addition salts thereof wherein R a  is CH 2  OH or CH 2  OCH 3  ; R is a branched member selected from the group consisting of fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t-butylcarbinyl, di-t-butylcarbinyl, 2-methylthio-2,4-dimethylpentan-3-yl, ##STR2## where at least one of R 3 , R 4 , R 5 , R 6  is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms, X is O, S, SO, SO 2 , C═O or CHOH; m is zero or 1-4, n and p are each zero, 1, 2 or 3 where the sum of n+p is not greater than 3 and the sum of the carbon atoms in R 3 , R 4 , R 5  and R 6  is not greater than six, and when both of R 3  and R 4  or R 5  and R 6  are alkyl they are methyl or ethyl, ##STR3## where one of R 7 , R 8 , R 9  is alkyl having from one to four carbon atoms and the remainder are hydrogen or alkyl having from one to four carbon atoms and the sum of the carbon atoms in R 7 , R 8  and R 9  is not greater than six, m and q are the same or different and each have the values previously defined for m; ##STR4## where each of R 12  and R 13  are methyl or ethyl, or R 12  is hydrogen and R 13  is alkyl having from one to four carbon atoms, Z is O or NH and t is 1 or 2, ##STR5## where W is 1-4, R 14  and R 16  are each alkyl having from one to four carbon atoms, R 15  is H, OH, methyl or ethyl and the sum of the carbon atoms in R 14 , R 15  and R 16  is not greater than six and when both of R 14  and R 15  are alkyl they are methyl or ethyl, and ##STR6## where R 17  and R 19  are alkyl having from one to four carbon atoms, R 18  and R 20  are H or alkyl having one to two carbon atoms, A is OH and B is H, OH or CH 3  and taken together A and B are ##STR7## where the sum of the carbon atoms in R 17 , R 18 , R 19  and R 20  is not greater than six and when both of R 17  and R 18  or R 19  and R 20  are alkyl they are methyl or ethyl; 
     said amides are potent sweeteners having advantages over the prior art, edible compositions containing them, methods for their use in edible compositions and novel amide intermediates useful in their production.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 276,243, filedJune 26, 1981, now U.S. Pat. No. 4,399,163, which is acontinuation-in-part application of Ser. No. 201,745, filed Nov. 5,1980, now U.S. Pat. No. 4,411,925 which is a continuation-in-part ofapplication Ser. No. 113,800, filed Jan. 21, 1980 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to novel amides of L-aspartyl-D-serine andL-aspartyl-D-O-methylserine which are especially useful in view of theirpotent sweetening properties, novel methods for their use in foods andedible composition containing them.

2. Description of the Prior Art

In U.S. Pat. No. 3,492,131 certain lower alkyl esters ofL-aspartyl-L-phenylalanine were found to be up to 200 times as sweet assucrose and to be substantially free of bitter flavor notes whichdetracted from earlier artificial sweeteners such as saccharin. Thesecompounds were subsequently found to have only limited stability inaqueous systems due to diketopiperazine formation especially at theneutral-acidic pH conditions prevalent in most food systems.

Mazur et al., J. Med. Chem., 16, 1284 (1973) has disclosed that loweralkyl esters of L-aspartyl-D-alanine and certain homologs thereof,especially L-aspartyl-D-alanine isopropyl ester, have sweetnesspotencies of up to 125 times sucrose.

Sukehiro et al., Seikatsu Kagaku, 11, 9-16 (1977); Chem. Abstr., 87,168407h (1977) has disclosed certain amides of L-aspartyl-D-alanine ofthe formula ##STR8## where R¹ is methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, secondary butyl, cyclohexyl or the carbon residue ofthe methyl esters of glycine, d-alanine or l-alanine. The most potentcompounds were those wherein R¹ is one of the above butyl groups orcyclohexyl, having respectively, 100-125 and 100 times the sweetness ofsucrose. Since the n-butylamide was found to have 125 times thesweetness of sucrose and the isobutyl and secondary butyl amides are100× sucrose, it was concluded that the potency of these amides isaffected mainly by the number of carbon atoms in the alkyl group, R¹,and that structural isomerism in the alkyl group has little effect onthe sweetness potency.

Esters of L-aspartyl-D-serine and L-aspartyl-D-threonine have been foundby Ariyoshi et al., Bull. Chem. Soc. Japan, 47, 326 (1974) to be sweeterthan the corresponding esters of L-aspartyl-D-alanine andL-aspartyl-D-2-aminobutyric acid, respectively. The most potent of theseesters, L-aspartyl-D-serine n-propyl ester, was 320 times as sweet as a5% sucrose standard.

U.S. Pat. No. 3,971,822 discloses esters of L-aspartyl-D-alaninol withcarboxylic acids, including 2-methylbutyric, cyclopropanecarboxylic,cyclobutanecarboxylic and 2-methylcyclobutanecarboxylic acids. Theesters with cyclopropane- and cyclobutanecarboxylic acids were 200× and220× sucrose, respectively. The ester with 2-methylcyclobutanecarboxylicacid was only 160× sucrose. Corresponding L-aspartyl-D-serinol estersare also disclosed, the sweetest of which, the ester with propionicacid, is 160× sucrose.

U.S. Pat. No. 3,959,245 and U.S. Pat. No. 3,907,766 disclose,respectively, L-aspartylaminomalonic acid methyl 2-methylcyclohexyldiester, and the corresponding alkyl fenchyl diester. The former isreported to be 6600× sucrose, the latter 4200-33,000× sucrose. In arelated publication by the inventors, Chem. Pharm. Bull., 24, 2112(1976), a series of L-aspartylaminomalonic acid diesters is disclosed,one of the ester groups being methyl or ethyl and the other being one ofa variety of branched alkyl and cycloalkyl groups.

SUMMARY

In our copending application, Ser. No. 201,745, filed Nov. 5, 1980, itwas found that it is not merely the size of the amide substituent thatis critical for a high degree of sweetness in L-aspartyl-D-alanineamides, but, to the contrary, it is the precise spatial arrangement ofthe amide substituent, R, that is critical. Certain L-aspartyl-D-alanineamides which are branched at the alpha carbon atom (the carbon atombearing the amide nitrogen atom) and also branched again at one or bothof beta and beta' carbon atoms were found to have significantadvantages.

The present invention provides certain novel branched amides ofL-aspartyl-D-serine and L-aspartyl-D-O-methylserine dipeptides whichhave unexpectedly high sweetness potency and are free from undesirableflavor qualities at conventional use levels. They have also been foundto have surprisingly high stability both in solid form and in aqueoussystems over the pH range found in most food systems even at theelevated temperatures used in baking and conventional food processing.

The novel compounds of the invention are the L-aspartyl-D-amino aciddipeptide amides of the formula ##STR9## and the physiologicallyacceptable cationic and acid addition salts thereof, wherein R^(a) isCH₂ OH or CH₂ OCH₃, and R is a branched member selected from the groupconsisting of fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl,d-ethyl-t-butylcarbinyl, di-t-butylcarbinyl,2-methylthio-2,4-dimethylpentan-3-yl, ##STR10## where at least one ofR³, R⁴, R⁵, R⁶ is alkyl having from one to four carbon atoms and theremainder are hydrogen or alkyl having from one to four carbon atoms; Xis O, S, SO, SO₂, C═O or CHOH; m is zero, 1, 2, 3 or 4; n and p are eachzero, 1, 2 or 3 and the sum of n+p is not greater than 3; the sum of thecarbon atoms in R³, R⁴, R⁵ and R⁶ is not greater than six and when bothof R³ and R⁴ or R⁵ and R⁶ are alkyl they are methyl or ethyl; ##STR11##where m is as defined above, one of R⁷, R⁸, R⁹ is alkyl having from oneto four carbon atoms and the remainder are hydrogen or alkyl having fromone to four carbon atoms and the sum of the carbon atoms in R⁷, R⁸ andR⁹ is not greater than six; ##STR12## where m and q are the same ordifferent and each have the values previously defined for m; ##STR13##where each of R¹² and R¹³ are methyl or ethyl, or R¹² is hydrogen andR¹³ is alkyl having from one to four carbon atoms, Z is O or NH and t is1 or 2; ##STR14## where w is 0, 1, 2, 3 or 4, R¹⁴ and R¹⁶ are each alkylhaving from one to four carbon atoms, R¹⁵ is hydrogen, OH or alkylhaving from one to two carbon atoms, where the sum of the carbon atomsin R¹⁴, R¹⁵ and R¹⁶ is not greater than six and when both of R¹⁴ and R¹⁵are alkyl they are methyl or ethyl; and ##STR15## where R¹⁷ and R¹⁹ arealkyl having from one to four carbon atoms, R¹⁸ and R²⁰ are hydrogen oralkyl having from one to two carbon atoms, taken separately, A is OH andB is hydrogen, OH or methyl and when taken together A and B are##STR16## where the sum of the carbon atoms in R¹⁷, R¹⁸, R¹⁹ and R²⁰ isnot greater than six and when both of R¹⁷ and R¹⁸ or R¹⁹ and R²⁰ arealkyl they are methyl or ethyl.

While the preferred sweeteners of the invention are those dipeptideamides of formula (I) wherein the aspartylamino acid dipeptide moiety isderived from L-aspartic acid and a D-amino acid, R^(a) CH(NH₂)COOH, alsoincluded within the scope of the invention are mixtures containing themost preferred L-aspartyl-D-amino acid amides of formula (I) wherein oneor both of the aspartyl or the other amino acid (i.e., serine orO-methylserine) moieties is racemic such as e.g.,

DL-aspartyl-D-serine amides,

DL-aspartyl-DL-serine amides,

L-aspartyl-DL-serine amides,

L-aspartyl-DL-O-methylserine amides,

DL-aspartyl-DL-O-methylserine, and

DL-aspartyl-D-O-methylserine amides.

Those compounds of formula (I) wherein the aspartyl moiety is entirelyof the D-configuration or the other amino acid moiety is entirely of theL-configuration have little or no sweetness.

An especially preferred group of L-aspartyl-D-amino acid amides offormula (I) are those wherein R is an acyclic member selected from thegroup consisting of diisopropylcarbinyl, d-methyl-t-butylcarbinyl anddi-t-butylcarbinyl.

Another especially preferred group of L-aspartyl-D-amino acid amides offormula (I) are those wherein R is a member selected from the groupconsisting of ##STR17## wherein R³ -R⁹, R¹² -R²⁰ ; A, B, X, Z, m, n, p,q, t and w are as defined above; and more particularly preferred arethose compounds of formula (I) wherein R has one of the first fourvalues of the group immediately above.

Particularly preferred amides of formula (I) are the L-aspartyl-D-serineamides, i.e., those wherein R^(a) is CH₂ OH.

Examples of the more valuable L-aspartyl-D-amino acid dipeptide amidesof the invention include those of formula (I) wherein R is:

(-)fenchyl,

diisopropylcarbinyl,

d-methyl-t-butylcarbinyl,

di-t-butylcarbinyl,

2,6-diethylcyclohexyl,

2-methylcyclopentyl,

2-ethyl-6-methylcyclohexyl,

2-ethylcyclohexyl,

2-methylcyclohexyl,

2,2-dimethylcyclohexyl,

2-ethylcyclopentyl,

2-methyl-6-isopropylcyclohexyl,

2,2,6,6-tetramethylcyclohexyl,

2,2,4,4-tetramethyltetrahydrofuran-3-yl,

2,2,6-trimethylcyclohexyl,

2-isopropylcyclohexyl,

2,5-dimethylcyclopentyl,

2,6-dimethylcyclohexyl,

2-isopropylcyclopentyl,

2,2,5,5-tetramethylcyclopentyl,

t-butylcyclopropylcarbinyl,

2,2,4,4-tetramethylthietan-3-yl,

2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl,

2,2,4,4-tetramethyltetrahydrothiophene-3-yl,

3,5-dimethyltetrahydrothiapyran-4-yl,

2-t-butylcyclohexyl or

dicyclopropylcarbinyl;

Especially valuable sweeteners include the above compounds wherein R is:

di-t-butylcarbinyl,

2,2,6-trimethylcyclohexyl,

2-t-butylcyclohexyl,

2-isopropylcyclohexyl,

2,6-dimethylcyclohexyl,

2,5-dimethylcyclopentyl,

2-isopropylcyclopentyl,

2,2,5,5-tetramethylcyclopentyl,

2,2,4,4-tetramethyltetrahydrothiophene-3-yl,

t-butylcyclopropylcarbinyl,

dicyclopropylcarbinyl,

2,2,4,4-tetramethylthietane-3-yl or

2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl.

More especially preferred are those compounds of formula (I) wherein Ris:

2,2,5,5-tetramethylcyclopentyl,

2,2,4,4-tetramethyltetrahydrothiophene-3-yl,

t-butylcyclopropylcarbinyl,

dicyclopropylcarbinyl,

2,2,4,4-tetramethylthietan-3-yl, and

2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl.

Most particularly preferred compounds of formula (I) are those wherein:R^(a) is CH₂ OH and R is

dicyclopropylcarbinyl,

2,2,4,4-tetramethylthietan-3-yl,

2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl,

and those wherein R^(a) is CH₂ OCH₃ and R is

2,2,4,4-tetramethylthietan-3-yl and

2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl,

which have sweetness potencies of from 200-1200 times that of sucrose.

The invention further provides compositions for sweetening ediblematerials which comprises a sweetening amount of a compound of formula(I) and a nontoxic carrier. Most preferably preferred compositions arethose containing L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amide,L-aspartyl-D-serine N-(2,2,4,4-tetramethylthietane-3-yl)amide, the1,1-dioxo derivative of the latter.

Additionally, sweetened edible compositions comprising an ediblematerial and a sweetening amount of a compound of the invention, areprovided.

Also provided is a method for sweetening edible compositions whichcomprises adding thereto a sweetening amount of a compound of theinvention.

The invention further provides compositions for sweetening ediblematerials which comprises a sweetening amount of a mixture of a compoundof formula (I) and saccharin or a physiologically acceptable saltthereof.

Especially preferred such mixtures are those wherein in said compound offormula (I), R^(a) is CH₂ OH and R is dicyclopropylcarbinyl,2,2,4,4-tetramethylthietan-3-yl or2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl. Most particularly preferredare mixtures of L-aspartyl-D-serineN-(2,2,4,4-tetramethylthietan-3-yl)amide and said saccharin, especiallythose wherein said compound and said saccharin are present in a weightratio of from 1:1 to 1:8.

By physiologically acceptable salts of saccharin is meant the salts ofsaccharin with physiologically acceptable cations such as e.g., thesodium, potassium, calcium or ammonium salts.

By physiologically acceptable cationic salts of the compounds of theinvention is meant the salts formed by neutralization of the freecarboxylic acid group of the compounds of formula (I) by bases ofphysiologically acceptable metals, ammonia and amines. Examples of suchmetals are sodium, potassium, calcium and magnesium. Examples of suchamines are N-methylglucamine and ethanolamine.

By the term physiologically acceptable acid addition salts is meantthose salts formed between the free amino group of the compound offormula (I) and a physiologically acceptable acid. Examples of suchacids are acetic, benzoic, hydrobromic, hydrochloric, citric, fumaric,gluconic, lactic, maleic, malic, nitric, phosphoric, saccharic, succinicand tartaric acids.

The invention still further provides valuable novel intermediates,useful in preparation of the invention compounds of formula (I). Saidintermediates are the D-amino acid amides of the formula ##STR18## whereR^(a) is as previously defined and R^(c) is a member selected from thegroup consisting of fenchyl, diisopropylcarbinyl,d-methyl-t-butylcarbinyl, d-ethyl-t-butylcarbinyl, di-t-butylcarbinyl,cyclopropyl-t-butylcarbinyl, cyclopentyl-t-butylcarbinyl,dicyclopropylcarbinyl, ##STR19## where m₁ is 1, 2 or 3 and when m₁ is 1:R³⁰, R⁴⁰, R⁵⁰ and R⁶⁰ are each methyl, when m₁ is 2: R³⁰ is methyl,ethyl or isopropyl and R⁴⁰, R⁵⁰ and R⁶⁰ are each hydrogen or R³⁰ and R⁵⁰are each methyl and R⁴⁰ and R⁶⁰ are each hydrogen, and when m is 3:

(a) R³⁰ is isopropyl or t-butyl, R⁴⁰, R⁵⁰ and R⁶⁰ are each hydrogen,

(b) R³⁰ is ethyl, R⁵⁰ is methyl, R⁴⁰ and R⁶⁰ are each hydrogen, or

(c) R³⁰ and R⁴⁰ are each methyl and R⁵⁰ and R⁶⁰ are each hydrogen ormethyl, and ##STR20## where when n₂ and p₂ are each zero: R⁴¹ and R⁶¹are each methyl and X₂ is S, SO₂, C═O or CHOH, when n₂ is zero and p₂ is1: R⁴¹ and R⁶¹ are each methyl and X₂ is O, S, or SO₂, and when n₂ is 1and p₂ is 1: R⁴¹ and R⁶¹ are each hydrogen and X₂ is S or SO₂.

The suffix "carbinyl" as used herein denotes the moiety --CH--. Thus,for example, diisopropylcarbinyl is the group (i--C₃ H₇)₂ --CH-- anddicyclopropylcarbinylamine is (Δ)₂ CHNH₂.

DETAILED DESCRIPTION OF THE INVENTION

The instant dipeptide amides are conveniently manufactured by methodssuitable for coupling of amino acids. A preferred method for preparingthe dipeptide amides of formula (I) is outlined below. ##STR21## In theabove L-aspartic acid derivatives Q is one of the well knownamino-protecting groups which can be selectively removed such as thosedescribed by Boissonnas, Advances in Organic Chem., 3, 159-190 (1963).Particularly preferred amino-protecting groups are benzyloxycarbonyl andtert-butyloxycarbonyl. R¹⁰ is preferably an alkyl group having from oneto four carbon atoms or benzyl. The D-serine or D-O-methylserineemployed may be in the form of the free amino acid wherein R¹¹ ishydrogen, but is preferably a carboxyl-protected derivative wherein R¹¹may be the residue of an ester group such as methyl or ethyl, but ispreferably a silyl group such as trialkylsilyl, having from three totwelve carbon atoms. An especially preferred such group istrimethylsilyl for reasons of economy and efficiency.

In the first step of the above reaction sequence the diprotectedL-aspartic acid is condensed with the appropriate D-amino acid or acarboxy-protected derivative to provide the diprotected dipeptide offormula (II). While this step may be carried out with the diprotectedaspartic acid in the presence of condensing agents such as, for example,dicyclohexylcarbodiimide, it is preferred to employ an alphacarboxylactivated derivative of the diprotected aspartic acid. Preferred suchcarboxyl activated derivatives are the chloride, bromide, anhydride ormixed anhydride. Especially preferred for reasons of efficiency are themixed anhydrides of the above diprotected-L-aspartic acids with estersof chlorocarbonic acid, particularly the alkyl esters wherein said alkylhas from one to four carbon atoms. Most preferred mixed anhydrides arethose prepared from the methyl and ethyl esters of chlorocarbonic acidfor reasons of economy.

In one preferred method for preparing the compounds of formula (I),beta-benzyl-N-benzyloxycarbonyl-L-aspartic acid is reacted with ethylchlorocarbonate to form the corresponding mixed anhydride by methodsknown in the art. In a separate vessel the D-amino acid, R^(a)CH(NH₂)COOH, which is obtained from commercial sources or by resolutionof the racemic amino acid by known methods [see e.g. Yamada et al., J.Org. Chem., 38, 4408 (1973)], is converted to the trimethylsilyl esterby contacting the amino acid with an equimolar amount of trimethylsilylchloride in the presence of a reaction inert organic solvent; for thecase when R^(a) is CH₂ OH, two molar equivalents of silylating agent isordinarily employed. Suitable solvents for this purpose are, forexample, pyridine, dimethylformamide or dimethylacetamide; especiallypreferred is dimethylformamide.

In a typical reaction according to this method, the D-amino acid e.g.,D-O-methylserine, dissolved in dimethylformamide and an equimolar amountof trimethylchlorosilane is added at room temperature. In a separateflask beta-benzyl N-benzyloxycarbonyl-L-aspartic acid and a molar excessof an acid binding agent, preferably triethylamine are dissolved amixture of dimethylformamide and tetrahydrofuran and an equimolar amountof ethylchlorocarbonate is added at room temperature or below,preferably at about -25° to 25° C. and especially at about -10° to 0° C.to form the mixed anhydride. To this is added the solution of e.g.,D-O-methylserine trimethylsilyl ester, preferably at a temperaturewithin the same range. Reaction is ordinarily complete within one or twohours after which the reaction mixture is poured into water or aqueousacid, for example hydrochloric acid, and the product of formula (II)extracted with a water immiscible solvent, typically chloroform,methylene chloride or ethyl ether and isolated by standard methods. Thediblocked dipeptide (II) is ordinarily of sufficient purity for use inthe next step, but may be further purified if desired, for example bycolumn chromatography.

In the second step of this method the diblocked dipeptide (II) isreacted with an equimolar amount of primary amine of formula RNH₂ toprovide the corresponding diblocked dipeptide amide intermediate offormula (III) wherein R^(a), R, R¹⁰ and Q are as previously defined. Asin the first step, the carboxylic acid form of the reactant (II) can besuccessfully employed by use of condensing agents, for exampledicyclohexylcarbodiimide to provide the intermediates of formula (III).However, it is preferred to convert the compound of formula (II) to acarboxyl activated derivative, for example the chloride, bromide ormixed anhydride, the latter being preferred. Thus, employing theparticularly preferred compound of formula (II) wherein R¹⁰ is benzyland Q is benzyloxycarbonyl, the mixed anhydride is prepared. As above,the preferred anhydrides are those obtained from esters ofchlorocarbonic acid and the methyl and ethyl esters thereof areparticularly preferred. The mixed anhydrides of compound (II) areprepared employing reactants and conditions described above for thefirst step of this sequence. In a typical reaction the compound offormula (II) and triethylamine in approximately equimolar amounts arecombined in a reaction inert organic solvent, for exampletetrahydrofuran, the mixture cooled to about -10° C. andethylchlorocarbonate added to obtain the mixed anhydride. To this isthen added an equimolar amount of the amine of formula RNH₂ or asolution thereof, for example in the same reaction inert solvent and ata temperature in the range of from about -50° to 25° C. and preferablyat from -35° to -5° C. After the addition of the amine is complete, thereaction mixture is allowed to warm to about room temperature andmaintained at this temperature until reaction is substantially complete,ordinarily from about 1 to 20 hours. The desired intermediate of formula(II) is then isolated and purified, if desired, by the same methodsdescribed above for compound (II).

In the final step of this method the carboxyl protecting group, R¹⁰ andamino protecting group, Q, are removed to provide the desired sweetenersof formula (I).

The method selected for removal of protecting groups from the dipeptideamide of formula (III) will vary depending on a number of factors whichwill be apparent to those of skill in the art. Two important factors forsuch selection are the nature of the protecting groups R¹⁰ and Q, andthe nature of the amide substituent, R. For example, when R¹⁰ and Q are,respectively, the especially preferred groups benzyl andbenzyloxycarbonyl and R does not contain sulfur, a preferred method forremoving said protecting groups is, ordinarily, by hydrogenolysis.However, when R¹⁰ is benzyl or alkyl as defined above and Q istert-butyloxycarbonyl and R has any of the values above, it is ordinarlypreferred to remove the protecting groups by hydrolysis. A combinationof hydrolysis and hydrogenolysis is preferred in those cases wherein R¹⁰is alkyl, Q is benzyloxycarbonyl and R does not contain sulfur.

When hydrogenolysis is selected for removal of protecting groups fromthe intermediate of formula (III) it is preferred to carry out thereaction in the presence of a catalytic amount of a noble metalcatalyst, palladium being especially preferred, and in the presence of areaction inert solvent. Examples of such solvents include the loweralkanols, such as methanol, ethanol, isopropanol and n-butanol; ethers,such as tetrahydrofuran, ethyl ether, 1,2-dimethoxyethane anddiethyleneglycol dimethylether; esters such as ethyl acetate, methylpropionate and dimethylsuccinate; and dimethylformamide. Particularlypreferred such solvents are methanol and ethanol for reasons of economyand efficiency. While the hydrogenolysis may be carried out successfullyat higher pressures and temperatures, use of pressures of from about1-10 atmospheres and room temperature are preferred for reasons ofeconomy and convenience. At the preferred temperature and pressure thereaction is ordinarily complete in from about 30 minutes to about sixhours, after which the catalyst is removed, typically by filtration, thesolvent evaporated and the resulting product purified, if desired, bystandard methods, for example by recrystallization or columnchromatography.

When hydrolysis is selected for removal of one or both of protectinggroups R¹⁰ and Q any of the well known methods for alkaline hydrolysisor acid hydrolysis of esters and the like may be employed with somesuccess. However, when blocking groups R¹⁰ are to be removed byhydrolysis, alkaline hydrolysis is preferred, and especially preferredconditions are use of at least an equivalent amount of a strong base,for example, sodium hydroxide or potassium hydroxide in the presence ofwater and a lower alkanol, particularly methanol or ethanol, at or aboutroom temperature. Under these preferred conditions hydrolytic removal ofthe R¹⁰ group is ordinarily complete in a few hours or less.

When the amino protecting group Q is tert-butyloxycarbonyl it ispreferred to use acid hydrolysis for its removal. Especially preferredis dilute aqueous hydrochloric acid in the presence of methanol orethanol and heating the mixture at reflux. Under these conditionshydrolysis is ordinarily complete in a few hours or less.

Isolation of the products of formula (I) after removal of protectinggroups by any of the above hydrolysis methods employs standardprocedures known in the art. For example, after acid hydrolysis thereaction mixture is evaporated to remove solvent, the aqueous residuewashed with a water immiscible non-polar solvent, for example, ethylether or chloroform after which the aqueous layer is made alkaline andthe product extracted with a water-immiscible solvent such as, forexample, ethyl acetate and the product obtained by evaporation ofsolvent. If desired, the product can be further purified, for example,by recrystallization or column chromatography. When alkaline hydrolysisto remove a protecting group R¹⁰ is followed by hydrogenolysis to removethe amino protecting group Q, the reaction mixture from the alkalinehydrolysis is preferably neutralized by addition of acid, for example,hydrochloric acid, and the neutralized reaction mixture subjected tohydrogenolysis as described above.

A second preferred method for manufacture of the instant compounds offormula (I) is shown below. ##STR22## R^(a), R, R¹⁰ and Q are as definedabove.

The amino protected D-amino acid or its carboxyl activated derivative isreacted with an equimolar amount of amine RNH₂ employing methods andconditions described above for the preparation of intermediates (II) and(III) to obtain an amino protected D-amino acid amide of formula (IV).The protecting group Q is removed by hydrogenolysis or hydrolysis asdescribed above and the resulting free amino amide (V) is condensed witha diblocked L-aspartic acid derivative or a carboxyl activatedderivative thereof, as described above for the preparation ofintermediates of formula (II), to provide the diblocked dipeptide amideof formula (III) from which the desired sweetener of formula (I) isobtained as previously described.

In a modification of this method an intermediate of formula (IV) whereinR contains a cyclic or acyclic sulfide moiety (--S--) may be oxidized tothe corresponding sulfoxide or sulfone prior to its conversion tointermediate (V) and subsequent reactions as described above, to providecompounds of formula (I) wherein R is a sulfoxide or sulfone.

In a third preferred method for preparing the compounds of the inventionthe D-amino acid amide of formula (V), described above, is reacted withL-aspartic acid N-thiocarboxyanhydride to provide directly the compoundsof formula (I). In carrying out this method the intermediate (V) in asuitable solvent is contacted with an equimolar amount of L-asparticacid N-thiocarboxyanhydride at a mildly alkaline pH at a temperature offrom about -25° to 10° C. to provide the compound of formula (I). Thealkaline pH for this reaction is provided by means of a strong base, forexample, sodium hydroxide or potassium carbonate. Suitable solvents forthis reaction are those that dissolve at least a portion of thereactants under the reaction conditions employed without reacting witheither reactant to an appreciable extent and allow the products formedin the reaction to be isolated with relative ease. Examples of suchsolvents for this reaction are water, tetrahydrofuran,1,2-dimethoxyethane, diethyleneglycol dimethylether, dimethylsulfoxide,dimethylformamide and combinations thereof; preferred solvents arewater, and its mixtures with tetrahydrofuran. A preferred alkaline pHrange for this reaction is from about 8 to 10 and a pH of about 9 isespecially preferred. An especially preferred temperature is in therange of about -10° to 0° C.

Under the preferred conditions mentioned above the reaction isordinarily complete in one to two hours. The product of formula (I) thenisolated by standard methods, for example, the pH of the reactionmixture is adjusted to the isoelectric pH of the product, ordinarilyabout pH 5.0-5.6, to precipitate the product of formula (I), the bulk ofthe solvent removed by evaporation or filtration and the crude materialslurried with an organic solvent, for example, methanol, ethanol, ethylether, ethyl acetate or mixtures thereof. The product of formula (I) isthen isolated, by filtration for example. It may be further purified, ifdesired, by, e.g., recrystallization or column chromatography.

The sweetness potency of the instant compounds was determined bycomparison of their gustatory sweetnesses with sucrose. Aqueoussolutions of the compound of formula (I) diluted to a suitable range ofconcentrations were compared with a sucrose standard by an expert tastepanel. Comparisons were generally made with aqueous sucrose solutions of7-9%, i.e., 7-9 g. per 100 ml. Higher sucrose concentrations have adistinctive mouthfeel which may influence results and lower sucroseconcentration are not indicative of normal use situations. If, forexample a 0.014% solution of the compound of formula (I) is judged to beequally as sweet as a 7% sucrose solution, then the sweetness potency ofthat compound is 7/0.014=500×sucrose. All of the sweetness potencyvalues stated herein for the compounds of the invention were determinedby this method. At threshold concentrations (i.e., the lowestconcentration at which sweetness is first noticed, which for sucrose isordinarily at concentrations in the range of 2-3%), the potency of asweetener, such as the compounds of the invention, is generally twicethat observed by comparison of its gustatory sweetness with 7-9%solutions of sucrose.

The requisite amines of formula RNH₂ wherein R is as previously definedare either commercially available or can be obtained from readilyavailable precursors. For example, the 2-alkylcyclohexylamines and2,6-dialkylcyclohexylamines can be obtained by catalytic hydrogenationof the corresponding alkyl substituted anilines. Many of the amines areobtained by reductive amination of the corresponding ketone using avariety of conditions known in the art. For example, reductive aminationby the well known Leuckhart reaction employing formic acid and formamideas reducing agents, see for example, the review in Organic Reactions,Wiley and Sons, New York, Vol. 5, p. 301, 1949, may be employed.Alternatively, the appropriate ketone can be reductively aminatedemploying sodium cyanoborohydride and ammonium acetate see for example,J. Amer. Chem. Soc., 93, 2897 (1971), or by means of ethanolic ammoniain the presence of a hydrogenation catalyst such as Raney nickel,platinum or palladium, see, for example, Organic Reactions, 4, 174(1948). Many of the amines of formula RNH₂ are obtained from thecorresponding ketones by formation of an intermediate oxime formed byreacting the ketone with hydroxylamine or its salts under conditionswell known in the art. The oxime intermediate is then reduced bycatalytic hydrogenation or by means of sodium in the presence of a loweralkanol at elevated temperature. A particularly preferred method,especially useful for reducing oximes of sulfur-containing ketones,employs reduction of the oxime in ethanol and a molar excess of sodiumat the reflux temperature of the mixture.

The requisite ketone precursors of the amines RNH₂ are eithercommercially available, known in the art or prepared by known methods.For example, the ketones of formula (VI) and (VII) ##STR23## where R³,R⁴, R⁵, R⁶, X, m, n and p are as defined above, except those of formula(VII) wherein X is C═O, may be obtained by alkylation of thecorresponding compounds wherein R³, R⁴, R⁵ and R⁶ are each hydrogen toprovide compounds of the above formula wherein from one to all of R³,R⁴, R⁵, R⁶ are alkyl as defined above. The alkylation is carried out,for example, employing alkylating agents such as the appropriate alkylhalide or alkyl sulfate under neutral or alkaline conditions provided bystrong bases, for example, sodium hydride or sodium amide. Using thesame method compounds of the formula (VI) and (VII) wherein only 1, 2 or3 of the substituents alpha to the keto group are alkyl can be convertedto compounds of the same formula wherein from two to four of R³, R⁴, R⁵,R⁶ are alkyl. Gem-dialkyl compounds of formula (VI) and (VII) whereineither R³ and R⁴ or R⁵ and R⁶ are said alkyl can be obtained from theappropriate monoalkyl compound by blocking the unsubstitutedalpha-position prior to alkylation and subsequent removal of theblocking group. For example, 2,2-dimethylcyclohexanone may be obtainedby condensation of 2-methylcyclohexanone with ethylformate in thepresence of sodium methoxide and the resulting intermediate alkylated asoutlined below. ##STR24##

Ketones of formula (VI) or (VII) wherein one or both of R³ and R⁵ arepropyl or butyl may be obtained by condensation of the correspondingalpha-unsubstituted compound with the appropriate aldehyde or ketoneunder alkaline conditions to an intermediate alpha- oralpha,alpha'-alkylidene ketone which can then be hydrogenated to providethe desired ketone.

The requisite cyclobutanones are obtained by methods described by Coniaet al., Bull. Soc. chim. France, 726 (1963) and Conia, Ind. chim. Belge,31, 981 (1966).

An alternative method for preparing the ketones of formula (VI) and(VII) involves a cyclization of an acyclic precursor. For example, bymeans of the well known Dieckmann cyclization of dicarboxylate estersand subsequent hydrolysis and decarboxylation; see e.g., ModernSynthetic Reactions, W. A. Benjamin, Menlo Park, Cal., 1972, p. 740. Thealpha-keto esters produced, especially those with no otheralpha-substituent, can also be alkylated prior to hydrolysis anddecarboxylation, if desired. This reaction can also be used to provideketones (VI) and (VII) which are unsubstituted at the carbons adjacentto the carbonyl group which can be alkylated as described above.

For preparation of diketones of formula (VII) wherein X is C═O the ketogroup of acyclic ketodicarboxylate ester precursor is converted to aketal or thioketal, e.g., dimethyl ketal, diethylthio ketal,ethylenedioxy ketal or ethylenedithio ketal, prior to Dieckmanncyclization. Ester group hydrolysis and decarboxylation affords aketo-ketal which may be converted to the corresponding amino ketal, bymethods described above, followed by hydrolysis of the ketal group bymethods well known in the art. The resulting amino ketone can behydrogenated, if desired, to the corresponding hydroxyamine (X=CHOH) byknown methods, e.g. by reduction with sodium borohydride.

2,2,4,4-Tetraalkyl-3-hydroxycyclobutylamines are prepared from thecorresponding 1,3-diones by the method of U.S. Pat. No. 3,125,569.

The amines of formula ##STR25## where X is CHOH and R³ -R⁶, n and p areas defined above, or N-protected derivatives thereof e.g.,N-benzyloxycarbonyl derivatives, may be oxidized, e.g. by chromiumtrioxide, to the corresponding compounds wherein X is C═O.Alternatively, the hydroxyamine may be reacted first with e.g., acarboxyl activated derivative of an N-protected D-O-methylserine and theresulting intermediate of formula (IV) wherein R is saidhydroxy-containing group, oxidized, e.g., with chromium trioxide, toprovide the corresponding ketone. The resulting ketone of formula (IV)is then converted to the desired product of formula (I) where R is aketo-containing group as desired above.

Certain of the ketones of formula (VII) are also obtained from acyclicprecursors derived from ketones of the formula (VIII) wherein R³, R⁴, R⁵and R⁶ are ##STR26## as previously defined. For example four-memberedketones of formula (VII) where X is O or S are obtained by brominationof (VIII) with two moles of bromine and the resultingalpha,alpha'-dibromo compound cyclized with, e.g., sodium hydroxide toprovide an oxetanone or hydrogen sulfide to provide a thietanone. Thecorresponding five-membered ring ketones (VII) are obtained when (VIII)is first reacted with formaldehyde to provide an intermediatealpha-hydroxymethyl compound which is then brominated at thealpha'-position and cyclized with sodium hydroxide or hydrogen sulfideto provide the corresponding compounds of formula (VII) wherein X is Oor S, respectively.

Certain of the tetrahydropyran-4-ones and tetrahydrothiapyran-4-ones offormula (VII) are obtained by adding the elements of water or hydrogensulfide to the appropriately substituted divinylketone.

Ketone intermediates of formula (IX) which may be converted to aminesvia the oxime are obtained by methods outlined below where R¹⁷, R¹⁸, R¹⁹and R²⁰ are as defined above. ##STR27## The appropriately substitutedacetoacetic ester (X) is condensed with formaldehyde, e.g. underalkaline conditions, and the resulting hydroxymethylated intermediate(XI) is then cyclized, for example by heating in the presence of a mildacid or base with removal of ethanol as it forms.

Bromination of acetoacetic esters of formula (X) and subsequenttreatment of the product with, e.g. sodium hydroxide, provides ketonesof formula (XII) which are converted to the corresponding amine asdescribed above. ##STR28##

Alternatively, the ketolacetones (XII) can be prepared by the methoddescribed in Zeit. Chemie, 13, 11 (1973); Chem. Abstr., 78, 135596e(1973), by reaction of the appropriate cyclobutan-1,3-dione withhydrogen peroxide.

The dibromo derivative of (VIII), described above, can also be treatedwith alkali hydroxides, e.g. sodium hydroxide under mild conditions, toform the corresponding 1,3-dihydroxyketone which is converted to thecorresponding 1,3-dioxane-2,5-dione of formula (XIII) by reaction withphosgene. ##STR29## The 5-oximino intermediate of (XIII) upon treatmentwith sodium in ethanol as described above, provides the corresponding5-amino compound.

Treatment of a monobromo derivative of ketones of formula (VIII) with,e.g. ethyl malonate, and subsequent hydrolysis, decarboxylation andesterification of resulting product affords intermediates of formula(XIV) which serve as precursors of the ketones (XV) as shown below, forexample. ##STR30## The ketolactones (XV) are then converted to thecorresponding 4-amino compound, e.g. by reduction of the oxime, asdescribed above.

The 1,3-dibromoketone derivatives of (VIII), described above, also canbe converted to the corresponding 1,3-dimercaptoketone by reaction withat least two moles of sodium hydrosulfide. Treating the dimercaptoketonewith reagents such as iodine, hydrogen peroxide or hypochlorous acidunder disulfide forming conditions, well known in the art provides theketones of formula XVI which are converted to amines by reduction of theoxime employing, e.g., sodium in ethanol. ##STR31##

Amines of formula (XVII) are provided directly, for example, by themethod of Nagase et al., Chem. Pharm. Bull. 17, 398 (1969) as shownbelow. ##STR32##

Use of ethylene oxide in place of formaldehyde in the first step of theabove reaction sequence affords the corresponding 3-amino-2-pyrones,##STR33##

Lactams corresponding to the above lactone intermediates or those offormula (IX), (XII), (XV) or (XVII), are obtained by reaction of theappropriate lactone with ammonia; for example, the above lactone iscontacted with an excess of anhydrous ammonia in ethanol and the mixtureallowed to stir overnight at ambient temperature to provide compounds ofthe formula ##STR34## Alternatively, certain lactam intermediates areprovided by the following reaction sequence. ##STR35##

The resulting ketones are then converted to the requisite amines bymethods described above.

The isomeric ketolactams are obtained by the following reactionsequence: ##STR36##

The corresponding 5-membered lactams are also obtained by the method ofU.S. Pat. No. 3,125,569: ##STR37##

Cyclic or open chain alpha-hydroxyketones oralpha,alpha'-dihydroxyketones of the formula ##STR38## where R¹⁴ -R²⁰,m, A and B are as previously defined are prepared by bromination withone or two moles of bromine and treatment of the bromo or dibromointermediate with an hydroxylic base, e.g., sodium hydroxide orpotassium hydroxide as described above. The reaction sequence isexemplified as follows: ##STR39##

Dicycloalkylketones (XVIII) and alkylcycloalkylketones (XIX) areprepared by the reaction of the appropriate acid halide and Grignardreagent employing conditions and reagents well known in the art, e.g.,as shown below. ##STR40##

Amines of formula RNH₂ where R is as previously defined are alsoobtained by the well known Hofmann reaction by conversion of theappropriate carboxamide with alkali metal hypohalite. This procedure isespecially useful for the preparation of cyclopropylamines. Thecorresponding cyclopropyl amides are obtained and converted to amines,e.g. as shown below. ##STR41##

The first step of the above sequence to form the cyclopropylcarboxylicacid ester is known in the art, see for example, Mescheryakov et al.,Chem. Abstr., 54, 24436 (1960).

The compounds of formula (I) or intermediate amides therefore, wherein Ris ##STR42## where X is SO or SO₂ are obtained from the correspondingcompounds wherein X is S by oxidation employing reagents and conditionsknown to form sulfoxides and sulfones from sulfides. Alternatively, theappropriate ketone of formula (VII) where X is S or the amine derivedfrom said ketone, as described above, can be oxidized to the sulfoxideor sulfone prior to coupling to form the dipeptide amide of formula (I).Preferred reagents and conditions for such oxidation of sulfides includeuse of hydrogen peroxide in a solvent, for example, acetic acid oracetone. When equimolar amounts of reactants are employed the product isthe sulfoxide, which is readily converted to the corresponding sulfoneby an additional mole of peroxide. Other preferred oxidants arepotassium permangante, sodium metaperiodate or chromic acid, forpreparation of the sulfones, and m-chloroperbenzoic acid. The latterreagent being especially useful for conversion of the above thioketones(VII) to the corresponding sulfoxide employing one mole of this reagent,or the sulfone when two moles of the peracid are employed.

The compounds of formula (I) and the physiologically acceptable saltsthereof provide advantages as sweetening agents in view of their highpotency, their physical form and stability. They are, ordinarily,crystalline, non-hygroscopic, water soluble solids. They are uniquelycharacterized by possessing a sweet taste, devoid of undesirable harshor bitter flavor qualities at ordinary use levels. They can be usefullyemployed to impart sweetness to edible materials. The term "ediblematerials" as used herein signifies all non-toxic substances consumableby humans or other animals, in solid or liquid form. Illustrative ofsuch substances are: foods, including foodstuffs, prepared food items,chewing gum and beverages; food additives, including flavoring andcoloring agents as well as flavor enhancers; and pharmaceuticalpreparations.

The compounds of the invention can be prepared in a variety of formssuitable for utilization of sweetening agents. Typical forms which canbe employed are solid forms such as powders, tablets, granules anddragees; and liquid forms such as solutions, suspensions, syrups,emulsions as well as other commonly employed forms particularly suitedfor combination with edible materials. These forms can consist of thecompounds of formula (I) or their physiologically acceptable saltseither apart or in association with non-toxic sweetening agent carriers,i.e. non-toxic substances commonly employed in association withsweetening agents. Such suitable carriers include liquids such as water,ethanol, sorbitol, glycerol, citric acid, corn oil, peanut oil, soybeanoil, sesame oil, propylene glycol, corn syrup, maple syrup and liquidparaffin, and solids such as lactose, cellulose, starch, dextrin,modified starches, polysaccharides such as polydextrose (see, e.g. U.S.Pat. No. 3,766,165 and U.S. Pat. No. 3,876,794), calcium phosphate(mono-, di- or tri-basic) and calcium sulfate.

Likewise useful and compatible are compositions containing a compound ofthe invention combined with a known sweetening agent such as, forexample, sucrose, saccharin, cyclamate, L-aspartyl-L-phenylalaninemethyl ester and the like, useful for sweetening edible materials.Especially useful are the mixtures of compounds of formula (I) andsaccharin or a physiologically acceptable salt thereof, e.g., thesodium, potassium, calcium or ammonium salt of saccharin. In saidmixtures with saccharin the compounds of formula (I) reduce orcompletely mask the well known, undesirable bitter aftertaste of thesaccharin.

Particularly useful such sweetener compositions are those containingsaccharin in admixture with compounds of formula (I) which are at least400 times as sweet as sucrose, especially those wherein R^(a) is CH₂ OHand R is dicyclopropylcarbinyl, 2,2,4,4-tetramethylthietan-3-yl or2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl. Most particularly preferredare such mixtures of saccharin and L-aspartyl-D-serineN-(2,2,4,4-tetramethylthietan-3-yl)amide, especially such mixtures whichcontain the latter compound of formula (I) and saccharin in a weightratio in the range of from 1:1 to 1:8. These mixtures are not onlypleasantly sweet tasting and appreciably devoid of bitter aftertaste,they are, unexpectedly, significantly sweeter than calculated bysummation of sweetness of the individual components of the mixture. Thatis, they exhibit a synergist effect, being up to 50% sweeter thancalculated. In mixtures of saccharin or its salts andL-aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide in ratiosoutside the above range the synergist effect is considerably reduced.

The invention also provides sweetened edible compositions comprising anedible material and a sweetening amount of a compound of formula (I), aphysiologically acceptable salt thereof alone or in combination with anon-toxic carrier or known sweetening agent. Examples of specific ediblematerials which provide such sweetened edible compositions include:fruits, vegetables, juices, meat products such as ham, bacon andsausage; egg products, fruit concentrates, gelatins and gelatin-likeproducts such as jams, jellies, preserves, etc.; milk products such asice cream, sour cream and sherbet; icings, syrups including molasses;corn, wheat, rye, soybean, oat, rice and barley products such as bread,cereals, pasta, cake and cake mixes; fish, cheese and cheese products,nut meats and nut products, beverages such as coffee, tea, carbonatedand non-carbonated soft drinks, beers, wines and other liquors;confections such as candy and fruit flavored drops, condiments such asherbs, spices and seasonings, flavor enhancers such as monosodiumglutamate and chewing gum. The instant sweeteners are also of use inprepared packaged products such as dietetic sweeteners, liquidsweeteners, granulated flavor mixes which upon reconstitution with waterprovides non-carbonated drinks, instant pudding mixes, instant coffeeand tea, coffee whiteners, malted milk mixes, pet foods, livestock feed,tobacco and consumable toiletries such as mouth washes and toothpaste aswell as proprietary and non-proprietary pharmaceutical preparations andother products of the food, pharmaceutical and sundry industries.

Especially preferred sweetened edible compositions are carbonatedbeverages containing one or more of the instant sweeteners.

The L-aspartyl-D-amino acid dipeptide amides of the instant inventionand the corresponding dipeptide amides of our copending application Ser.No. 201,745, filed Nov. 5, 1980, of the formula ##STR43## where R is asdefined herein and R^(a') is methyl, ethyl, n-propyl or isopropyl, arealso useful in the applications disclosed in the art forL-aspartyl-L-phenylalanine methyl ester and analogs thereof. Forexample, they are useful in the same funtions disclosed in the followingpatents and patent applications for L-aspartyl-L-phenylalanine methylester. In these uses they have the advantages disclosed for thedipeptide ester as well as their previously mentioned advantages instability and potency:

    ______________________________________                                        U.S. Pat. Nos.:                                                               3,642,491            3,971,857 3,865,957                                      3,761,288            3,982,023                                                3,800,046            4,001,456                                                3,818,077            4,004 039                                                3,829,588            4,007,288                                                3,875,311            4,031,258                                                3,875,312            4,036,992                                                3,886,295            4,051,268                                                3,922,369            4,059,706                                                3,934,048            4,122,195                                                3,947,600            4,139,636                                                3,955,000            4,143,170                                                3,956,507            4,153,737                                                Canadian Patent Nos.:                                                         1,026,987                                                                     1,027,113                                                                     1,028,197                                                                     1,043,158                                                                     1,046,840                                                                     Netherlands Patent Application Nos.                                           73-04,314                                                                     73-11,307                                                                     75-14,921                                                                     76-05,390                                                                     76-08,963                                                                     West German Offenlegungsschrift Nos.:                                         2,438,317                                                                     2,456,926                                                                     2,509,257                                                                     2,518,302                                                                     2,609,999                                                                     2,646,224                                                                     2,713,951                                                                     Belgian Pat. Nos.:                                                            830,020                                                                       838,938                                                                       863,138                                                                       882,672                                                                       Great Britian Patent No. 1,464,571;                                           Japan Kokai No. 77-04,176;                                                    French Patent No. 2,338,651 and                                               Swiss Patent No. 590,615.                                                     ______________________________________                                    

The invention is further illustrated by the following examples.

EXAMPLE 1 L-Aspartyl-D-serine N-(dicyclopropylcarbinyl)amide ##STR44##

A solution of 4.41 g. (0.042 mole) D-serine in 21 ml. of 2 N sodiumhydroxide was cooled to 5° to 10° C., adjusted to pH 10.0-11.5 withconcentrated hydrochloric acid and 6.9 ml. (0.048 mole) benzylchloroformate was added in increments over 1.5 hours with simultaneousaddition of 2 N sodium hydroxide to maitain the mixture within the aboverange of pH. The mixture was stirred overnight at room temperature,washed with ethyl ether and the aqueous phase acidified (pH 2.5-3.0)with 6 N hydrochloric acid. Extraction with ethyl acetate, washing theextracts with brine and drying (MgSO₄), afforded 3.14 g. of product as acolorless solid which was recrystallized from 20 ml. ethyl acetate toyield 2.64 g. of product, R_(f) 0.43 [thin layer chromatography (TLC),ethyl acetate/hexane/acetic acid, 9:9:2, by volume]. ##STR45##

To a slurry of 2.4 g. (0.01 mole) of N-Cbz-D-serine, obtained in Part A,in 75 ml. chloroform was added 1.1 ml. (0.01 mole) N-methylmorpholine. Asolution was obtained which was cooled to -12° C. To this was added 0.96ml. (0.01 mole) ethyl chloroformate, the mixture stirred at -10° C. forfive minutes, a solution of 1.11 g. (0.01 mole) dicyclopropylamine in 5ml. chloroform was added and stirring continued for five minutes at -15°C. The reaction mixture was allowed to warm to room temperature, washedsuccessively with 0.5 N hydrochloric acid, 5% sodium bicarbonatesolution, water and the chloroform evaporated in vacuo. The aqueouswashes were combined and extracted with ethyl acetate. The ethyl acetateextracts were combined with the residue obtained by evaporation ofchloroform and the ethyl acetate was dried (MgSO₄) and evaporated invacuo to afford a white solid which was dried in the vacuum ovenovernight to give 3.2 g. of the desired product, R_(f) 0.54 which wasused in the next step. ##STR46##

The 3.2 g. (9.6 mmole) N-Cbz-amide, obtained in Part B, was dissolved in70 ml. methanol, 1.0 g. 5% Pd/C catalyst added and the mixturehydrogenated at 60 psi (4.2 kg./cm.²) for 30 minutes. The catalyst wasremoved by filtration and the filtrate evaporated in vacuo to yield 1.93g. of product as a soap-like solid. ##STR47##

A mixture of 3.4 g. (9.5 mmole) beta-benzylN-benzyloxycarbonyl-L-aspartate, 1.0 ml. (9.5 mmole) N-methylmorpholineand 0.9 ml. (9.5 mmole) ethyl chloroformate was stirred at -15° to -10°C. for five minutes and a solution of 1.9 g. (9.5 mmole) D-serineN-dicyclopropylcarbinylamide, obtained in Part C, in 10 ml. chloroformwas added at -15° C. The resulting mixture was stirred at -10° C. forfive minutes, allowed to warm to ambient temperature and stirred for onehour. The reaction mixture was evaporated in vacuo to remove solvent,the residue taken up in ethyl acetate (250 ml.), washed in turn with 1 Nhydrochloric acid, 5% sodium bicarbonate solution, brine and dried overanhydrous magnesium sulfate. The solvent was evaporated in vacuo toobtain a gelatinous solid. This was taken up in 75 ml. hot ethylacetate. Upon cooling a crystalline solid was obtained which was driedin vacuo at 40° C. to yield 2.75 g. of the desired diprotected dipeptideamide as a fine white solid, R_(f) 0.30.

E. A mixture of 2.75 g. of the diprotected dipeptide amide, obtained inPart D, 200 ml. methanol and 1.0 g. 5% Pd/C catalyst was hydrogenated at60 psi (4.2 kg./cm.²) for one hour during which product precipitated.The catalyst/product mixture was filtered, the filter cake slurried in100 ml. hot water and filtered again. The combined filtrates wereevaporated to dryness, triturated with water, filtered and dried invacuo to afford 260 mg. of product as a fine white, fluffy solid, M.P.252°-254° C., R_(f) 0.58 (TLC, n-butanol/water/acetic acid 4:1:1,ninhydrin spray).

The filter cake from the hydrogenation was slurried in 50 ml. of 0.1 Nhydrochloric acid, the mixture filtered through diatomaceous earth(Supercel), the filtrate (pH 1.6) was adjusted to pH 5.9 with sodiumhydroxide solution, and the precipitated product collected by filtrationand dried in vacuo to yield an additional 800 mg. of product. Total stepyield, 68%.

Mass spectrum (m/e) 313 (M⁺).

Sweetness potency: 700×sucrose.

EXAMPLE 2 L-Aspartyl-D-serine N-(2,4-dimethyl-3-pentyl)amide ##STR48##

A mixed anhydride was prepared as follows: 1.0 g. (4.3 mole)N-benzyloxycarbonyl-D-serine was dissolved in 50 ml. tetrahydrofuran,cooled to -10° C. under a nitrogen atmosphere and 0.47 ml. (4.3 mmole)N-methylmorpholine and 0.41 ml. (4.3 mmole) ethyl chloroformate wereadded. The mixture was stirred at -10° C. for 30 minutes.

To the solution of mixed anhydride was added 495 mg. (4.3 mmole)2,4-dimethyl-3-aminopentane dissolved in a small amount of chloroform,the mixture stirred at -10° C. for 15 minutes and allowed to warm toroom temperature. Ethyl acetate (40 ml.) was added and the mixture waswashed with 1 N hydrochloric acid, sodium bicarbonate solution, brineand the organic layer was dried over anhydrous magnesium sulfate.Evaporation of solvent in vacuo gave 1.27 g. colorless solid which wastriturated with ethyl ether, filtered and air dried to afford 1.0 g. ofcolorless product, R_(f) 0.77 (TLC, ethyl acetate/hexane, 7:3 by volume,vanillin spray). ##STR49##

The above 1.0 g. of product was dissolved in 50 ml. methanol, 0.5 g. 5%Pd/C catalyst added and the mixture hydrogenated at 50 psi (3.52kg./cm.²) until hydrogen uptake ceased. Filtration and evaporation offiltrate gave 700 mg. of the desired product. ##STR50##

A solution of 1.36 g. (3.8 mmole) beta-benzylN-benzyloxycarbonyl-L-aspartate in 10 ml. tetrahydrofuran was cooled to-10° C. and 0.42 ml. (3.8 mmole) N-methylmorpholine was added. To thiswas added dropwise 0.36 ml. (3.8 mmole) ethyl chloroformate and theresulting mixture stirred at -10° C. for 5 minutes. Then 566 mg. (2.8mmole) D-serine N-(2,4-dimethyl-3-pentyl)amide (from Part B, above) in afew milliliters of tetrahydrofuran was added dropwise and stirringcontinued for 15 minutes. The reaction mixture was allowed to warm toroom temperature and evaporated in vacuo to afford a solid residue. Thiswas mixed with ethyl acetate, washed with 1 N hydrochloric acid and theorganic phase washed with 5% aqueous sodium bicarbonate, brine, dried(MgSO₄) and the solvent evaporated to afford 1.6 g. of product as anamorphous solid which was used in the next step.

D. To a solution of 2.7 g. of the diblocked dipeptide amide (preparationas described in Part C, above) in methanol was added 1.5 g. 5% Pd/Ccatalyst and the mixture was hydrogenated at 50 psi (3.52 kg./cm.²)until hydrogen uptake ceased. The catalyst was removed by filtration andthe filtrate evaporated in vacuo to a small volume and allowed to standat room temperature. The precipitated product was collected byfiltration and dried in vacuo to afford 342 mg. of colorless solid.

Sweetness, 180×sucrose.

EXAMPLE 3 L-Aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide##STR51##

The method is that described by Moroder et al., Z. Physiol. Chem. 357,1651 (1976), for preparing t-Boc-amino acids. To 10 ml. each of dioxaneand water was added 2.18 g. (10 mmole) di-t-butyl dicarbonate 1.6 ml.(11.5 mmole) triethylamine and 1.05 g. (10 mmole) D-serine. The mixturewas stirred for 30 minutes at room temperature and the dioxaneevaporated in vacuo. The aqueous residue was cooled in ice, ethylacetate was added and the mixture stirred while adding dilute potassiumbisulfate solution to pH 2-3. The aqueous layer was separated, extractedtwice with ethyl acetate and the combined extracts washed with water,dried (Na₂ SO₄) and the solvent evaporated in vacuo to yield 1.7 g. ofproduct as a viscous paste. ##STR52##

A mixed anhydride was prepared from 2.85 g. (14 mmole) ofN-t-butoxycarbonyl-D-serine, 1.55 ml. N-methylmorpholine, 1.34 ml. ethylchloroformate in 75 ml. methylene chloride at -12° to -10° C. by themethod of Example 1, Part B. To this mixture was added 2.01 g. (14mmole) of 3-amino-2,2,4,4-tetramethylthietane and stirring continued forfive minutes at -12° C. The product was isolated as described in Example1, Part B to afford 4 g. of a viscous liquid residue. The residue wasdissolved in 40 ml. methylene chloride, 12 ml. trifluoroacetic acid(d=1.480) was added and the mixture was stirred at room temperature forthree hours. The reaction mixture was made alkaline with 40% sodiumhydroxide solution, the organic layer separated, the aqueous layer wassaturated with sodium chloride and extracted with methylene chloride.The combined extracts were dried (MgSO₄) and concentrated to dryness invacuo to yield 2.21 g. amorphous off-white solid. Crystallization fromethyl ether/hexane gave 1.92 g. of product as a fine, white solid.##STR53##

A mixture of 2.3 g. (8.0 mmole) beta-t-butylN-t-butoxycarbonyl-L-asparate, 0.88 ml. (8.0 mmole) N-methylmorpholineand 0.77 ml. (8.0 mmole) ethyl chloroformate in 40 ml. methylenechloride was stirred at -12° C. for five minutes. A solution of 1.85 g.(8.0 mmole) D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amide in 5 ml.of the same solvent was added and stirring continued at -12° to -10° C.for ten minutes. The mixture was allowed to warm to room temperature,stirred for one hour at this temperature and the solvent evaporated. Theresidue was taken up in ethyl acetate, washed with dilute hydrochloricacid, sodium bicarbonate solution, brine, dried (MgSO₄) and the ethylacetate evaporated to afford 3.34 g. of amorphous solid. Crystallizationfrom ethyl ether/hexane gave 2.91 g. of colorless solid product, R_(f)0.70 (ethyl acetate/hexane, 7:3).

D. A solution of 2.4 g. (4.78 mmole) of the product obtained in Part C,above, in 60 ml. chloroform was fitted with a gas inlet tube andanhydrous hydrogen chloride bubbled through the solution. After fiveminutes, precipitation of solid was observed. The hydrogen chlorideaddition was continued for ten minutes, then the mixture was stirred atambient temperature for one hour and evaporated to dryness in vacuo. Theresidue was taken up in water, washed with chloroform, the pH adjustedto 5.6, washed again with chloroform, and the aqueous phase evaporatedin vacuo. Ethanol was added to the residue and the mixture evaporated todryness in vacuo. The residue was dissolved in 25 ml. hot water andallowed to cool. The precipitated product was collected by filtrationand dried in vacuo to yield 1.12 g. (67%) of product, M.P. 193°-196° C.R_(f) 0.32 (n-butanol/water/acetic acid, 4:1:1).

Analysis Calculated for C₁₄ H₂₅ N₃ O₅ S: C, 48.39; H, 7.25; N, 12.09; S,9.23. Found: C, 46.77; H, 7.48; N, 11.91; S, 8.82.

Sweetness potency, 1200×sucrose.

EXAMPLE 4 L-Aspartyl-D-serineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide ##STR54##

A. 3-Amino-2,2,4,4-tetramethylthietan-1,1-dioxide

A solution of 14.53 g. (0.1 mole) 3-amino-2,2,4,4-tetramethylthietaneand 64.17 g. (0.3 mole) sodium m-periodate in 500 ml. water was stirredovernight at room temperature. The reaction mixture was adjusted to pH13 with sodium hydroxide solution and the precipitated sodium iodateremoved by filtration. The filtrate was washed with 100 ml. ethyl ether,the aqueous phase extracted continuously with methylene chloride over 18hours, the extract dried (MgSO₄) and solvent evaporated in vacuo. Theresidual solid was recrystallized from ethyl acetate to provide 8.5 g.of product, M.P. 104°-106.5° C. A second crop of crystals was obtained,2.7 g., M.P. 103°-106° C. Total yield, 63%.

B. D-Serine N-(2,2,4,4-tetramethyl-1,1-dioxo-thietan-3-yl)amide

By the method of Example 1, Part B, 1.33 g. (6.5 mmole)N-benzyloxycarbonyl-D-serine, 0.715 ml. N-methylmorpholine, 0.62 ml.ethyl chloroformate and 1.15 g. (6.5 mmole)3-amino-2,2,4,4-tetramethylthietane-1,1-dioxane gave 2.3 g. ofN-benzyloxycarbonyl-D-serineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide as a viscous liquid,R_(f) 0.37 (ethyl acetate/hexane, 7:3). This liquid was dissolved inmethanol, 750 mg. of 5% Pd/C catalyst added and the mixture hydrogenatedby the method of Example 1, Part C. After filtering to remove thecatalyst, the methanol was evaporated in vacuo, the residue taken up in1 N hydrochloric acid and extracted with chloroform. The aqueous layerwas made alkaline with sodium hydroxide saturated with sodium chlorideand extracted continuously with chloroform overnight. Evaporation ofsolvent gave 1.54 g. of product as a viscous liquid which solidifiedupon standing, R_(f) 0.32 (m-butanol/water/acetic acid, 4:1:1).##STR55##

The diblocked dipeptide amide of the above formula was prepared on a 4.7millimolar scale employing the method of Example 1, Part D, with 1.7 g.beta-benzyl N-benzyloxycarbonyl-L-aspartate, 0.51 ml.N-methylmorpholine, 0.45 ml. ethyl chloroformate and 1.24 g. D-serineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide. The product, 2.45g., was obtained as a colorless amorphous solid. Two grams of thismaterial was purified by chromatography on 60 g. of silica gel, elutingwith ethyl acetate to afford 1.2 g. of amorphous solid product, R_(f)0.30 (ethyl acetate/hexane, 7:3).

D. A mixture of 1.2 g. of purified product from Part C, above, 75 ml.methanol and 0.6 g. of 5% Pd/C was hydrogenated at 80 psi (5.6kg./cm.²). When hydrogen uptake ceased, the catalyst was removed byfiltration, and the filtrate evaporated to afford a colorless solidresidue. The residue was taken up in water, washed with chloroform andthe aqueous layer evaporated in vacuo. The residual solid wascrystallized from ethanol to afford 255 mg. of the desired dipeptideamide as a fine white solid, M.P. 170-173, R_(f) 0.20. An additional 180mg. of product was obtained by reworking the filter cake from thehydrogenation.

Sweeetness potency: 850×sucrose.

EXAMPLE 5 D-O-Methylserine

A. N-Chloroacetyl-dl-O-methylserine

To 125 ml. water was added 59.55 g. (0.5 mole) dl-O-methylserine, themixture was stirred and 20 g. (0.5 mole) sodium hydroxide was added. Theresulting solution was cooled in ice and simultaneously, from twodropping funnels was added over one hour, a solution of 20 g. of sodiumhydroxide in 125 ml. water and 47.8 ml. (0.6 mole) chloroacetylchloride. The addition rates were adjusted to maintain the reactionmixture at pH 9.0-9.5. After the addition was completed, the resultingmixture was stirred for one hour at pH 9.0-9.5. The mixture was washedtwice with methylene chloride, the aqueous phase acidified to pH 1.5with concentrated hydrochloric acid while cooling in ice, saturated withsodium chloride and extracted several times with chloroform. Thecombined extracts were dried (MgSO₄) and the solvent evaporated invacuo. The residue was stirred with ethyl ether to precipitate a yellowsolid product which was collected by filtration and dried, 69.38 g.(71%). M.P. 104°-107° C., R.sub. f 0.23 (ethyl acetate/hexane/aceticacid, 9:9:2, phosphomolybdate spray). A second crop was obtained fromthe aqueous phase by adding more sodium chloride and extracting withchloroform. Evaporation of chloroform gave 3.65 g. of product. Totalyield 75%.

B. N-Chloroacetyl-D-O-methylserine

To 3000 ml. of water at 35°-37° C. was added 73.03 g. (0.37 mole)N-chloroacetyl dl-O-methylserine and the mixture adjusted to pH 7.18 byaddition of concentrated ammonium hydroxide. Water was added to make atotal volume of 3700 ml. To this was added 17 mg. of commercial porcinekidney aminoacylase, N-acylamino acid amidohydrolase; EC 3.5.1.14(Acylase I) having 1845 units/mg. (1 unit is defined as the amountrequired to hydrolyze 1 micromole of N-acetyl-L-methionine per hour atpH 7.0 and 25° C.). The amount of enzyme added was that calculated tohydrolyze the susceptible isomer in six hours. The resulting solutionwas maintained at 37°-38° C. for 28 hours with intermittent addition ofammonium hydroxide to maintain the pH at 7.1 to 7.2. An additional 5 mg.of enzyme was added after 24 hours. The hydrolysis mixture was acidifiedto pH 4.5 with glacial acetic acid, filtered through a 0.6 μm milliporefilter (type BD) and the filtrate evaporated in vacuo below 35° C. toreduce the total volume to 100-150 ml. The residual mixture wasacidified to pH 2.00 with hydrochloric acid and extracted several timeswith ethyl acetate and further extracted with chloroform. The separateorganic extracts were each washed with water, dried (MgSO₄) and solventevaporated in vacuo to afford a yellow liquid residue. Addition ofhexane and evaporation in vacuo induced crystallization. The ethylacetate extracts afforded 16.67 g. (46%) ofN-chloroacetyl-D-O-methylserine, M.P. 95°-96° C., [alpha]_(D) -15.5(C=1, 1 N NaOH). The chloroform extracts gave 4.61 g. (13%) of the sameproduct, M.P. 90°-94° C. (odor of chloroacetic acid). Both crops ofproduct showed a single spot upon thinlayer chromatography on silica gelplates, R_(f) 0.35; 9:9:2 ethyl acetate/hexane/acetic acid,phosphomolybdate spray.

C. To 16.67 g. (0.085 mole) N-chloroacetyl-D-O-methylserine was added 25ml. of 2 N hydrochloric acid and the mixture heated at reflux for threehours. The mixture was concentrated in vacuo, chasing any residualchloroacetic acid with additional water. The solid residue was washedwith ethyl ether and collected by filtration to afford 12.31 g. (93%)D-O-methylserine hydrochloride, M.P. 188°-190° C., [alph]_(D) -16.7°(C=0.7, CH₃ OH).

EXAMPLE 6 L-Aspartyl-D-O-methylserine N-(dicyclopropylcarbinyl)amide##STR56##

A solution of 12.31 g. (0.079 mole) D-O-methylserine in 40 ml. watercontaining 6.32 g. (0.158 mole) sodium hydroxide was cooled to 5°-10° C.and 11.74 ml. (0.0806 mole) benzyl chloroformate and 4 M sodiumhydroxide were added simultaneously at pH 8-9. The resulting mixture wasstirred until the pH remained at 8 without further addition of base.After washing with methylene chloride, the aqueous phase was acidifiedwith concentrated hydrochloric acid, extracted four times with methylenechloride, the extracts dried (MgSO₄) and solvent evaporated in vacuo.The viscous liquid residue was stirred with hexane and the precipitatedsolid collected by filtration to yield 18.6 g. of product (93%),[alpha]_(D) -2.7° (C=1, 1 N NaOH), R_(f) 0.43. ##STR57##

To a solution of 3.80 g. (0.015 mole)N-benzyloxycarbonyl-D-O-methylserine in 75 ml. methylene chloride wasadded 1.68 ml. (0.015 mole) N-methylmorpholine and the mixture cooled to-15° C. To this was added 1.43 ml. (0.015 mole) ethyl chloroformate, themixture stirred at -20° to -15° C. for ten minutes and 1.68 g. (0.015mole) dicyclopropylcarbinyl amine was added. The mixture was allowed towarm to room temperature and stirred for two hours. The resultingmixture was washed twice with 1 N sodium hydroxide, twice with 1 Nhydrochloric acid and dried over magnesium sulfate. Evaporation ofsolvent in vacuo gave 5.1 g. (98%) of the desired product, R_(f) 0.59upon silica gel TLC in 1:1 ethyl acetate/hexane, phosphomolybdate spray.

The structure of the product was confirmed by ¹ H-NMR spectroscopy.##STR58##

The 5.1 g. of N-benzyloxycarbonyl-D-O-methylserineN-(dicyclopropylcarbinyl)amide, obtained in Part B, above, washydrogenated by the procedure of Example 1, Part C, to afford 2.96 g.(95%) D-O-methylserine N-(dicyclopropylcarbinyl)amide as a liquid, R_(f)0.39; [alpha]_(D) -23.2 (C=0.7, 1 N HCl). The structure was confirmed by¹ H-NMR spectroscopy.

D. C₆ H₅ CH₂ OCOCH₂ CH(NHCbz)CONHCH(CH₂ OCH₃)CONHCH(Δ)₂

A mixture of 4.97 g. (13.9 mmole) beta-benzylN-benzyloxycarbonyl-L-aspartate, 1.55 ml. (13.9 mmole)N-methylmorpholine and 1.33 ml. (13.9 mmole) ethyl chloroformate werereacted as described in Example 1, Part D, to provide 7.43 g. (97%) ofthe diblocked dipeptide amide which was recrystallized twice from ethylacetate to give 4.25 g. of colorless product, R_(f) 0.45 (7:3 ethylacetate/hexane). The structure was verified by ¹ H-NMR.

E. Hydrogenation of the 4.25 g. of purified diblocked dipeptide amideobtained in Part D, above, by the procedure of Example 1, Part E, gave2.4 g. (95%) of the desired dipeptide amide, M.P. 215°-217° C. (dec.);[alpha]_(D) +37.6° (C=0.8, 1.2 N HCl); R_(f) 0.41.

Sweetness potency, 85×sucrose.

EXAMPLE 7 L-Aspartyl-D-O-methylserineN-2,2,4,4-tetramethylthietan-3-yl)amide ##STR59##

To a solution of 2.89 g. (18.6 mmole) D-O-methylserine hydrochloride in11 ml. water was added 6.48 ml. (46.5 mmole) triethylamine, 5.10 g.(20.7 mmole) 2-(t-butoxycarbonyloxyimino)-2-phenylacetonitrile("BOC-ON") and 11 ml. tetrahydrofuran. The mixture was stirred at roomtemperature overnight, diluted with 25 ml. water and washed with ethylacetate. The aqueous layer was acidified to pH 1.8 with 1 M hydrochloricacid, extracted with ethyl acetate (3×75 ml.), dried (MgSO₄) andevaporated in vacuo to afford 4.2 g. of product as a viscous liquid,R_(f) 0.65 (9:9:2 ethyl acetate/hexane/acetic acid, phosphomolybdatespray).

B. N-t-Boc-D-O-Methylserine N-(2,2,4,4-tetramethylthietan-3-yl)amide

To a solution of 4.2 g. (18.6 mmole) N-t-Boc-D-O-methylserine in 90 ml.methylene chloride was added 2.08 ml. N-methylmorpholine, the mixturecooled to -15° C. and 1.78 ml. ethyl chloroformate added. After stirringfor 8 minutes at -20° to -15° C., 2.70 g. (18.6 mole)3-amino-2,2,4,4-tetramethylthietane dissolved in 10 ml. methylenechloride was added at the same temperature and the mixture allowed towarm to room temperature. After stirring for two hours the mixture waswashed with dilute sodium hydroxide, dilute hydrochloric acid, driedover anhydrous magnesium sulfate and the solvent evaporated in vacuo toyield 6.04 g. (94%) of colorless solid, R_(f) 0.35 (3:7 ethylacetate/hexane, phosphomolybdate spray). The structure was verified by ¹H-NMR.

C. D-O-Methylserine N-(2,2,4,4-tetramethylthietan-3-yl)amide

To a solution of 6.04 g. (17.4 mmole) of N-t-Boc-D-O-methylserineN-(2,2,4,4-tetramethylthietan-3-yl)amide in 13.4 ml. methylene chloridewas added 6.7 ml. (87 mmole) trifluoroacetic acid (sp. gr. 1.480) andthe mixture was stirred at room temperature for three hours. Anadditional 1.0 ml. in 2 ml. methylene chloride was added and stirringcontinued for one hour. The reaction mixture was made alkaline with 40%(w/w) sodium hydroxide solution, the organic layer separated and theaqueous layer extracted several times with fresh methylene chloride. Thecombined extracts were dried (MgSO₄) and solvent evaporated in vacuo togive 4.29 g. of crude liquid product. This was taken up in 20 ml. 1 Nhydrochloric acid, washed with ethyl ether, the aqueous layer madealkaline with sodium hydroxide (40% w/w), saturated with sodium chlorideand extracted with methylene chloride. Evaporation of the extractsafforded 3.21 g. (75%) of the desired product, R_(f) 0.41; [alpha]_(D)-19.8° (C=0.8 1 N HCl). The structure of this product was verified byits ¹ H-NMR spectrum. ##STR60##

By employing 3.76 g. of product obtained by the procedure of Part C,above, the procedure of Example 3, Part C, was repeated on a 13millimolar scale using 50 ml. methylene chloride as solvent to afford5.0 g. (74%) of the desired diblocked dipeptide amide as a brittle foam,R_(f) 0.40 (ethyl acetate/hexane, 1:1; phosphomolybdate spray). Thestructure was verified by the ¹ H-NMR spectrum of the product.

E. Anhydrous hydrogen bromide was bubbled through a solution of 5.0 g.(9.7 mmole) of the diblocked dipeptide amide provided in Part D, above,while stirring at room temperature for one hour. The resulting mixturewas evaporated to dryness in vacuo and the resulting yellow solidresidue dissolved in water. The solution was washed twice with ethylether, once with methylene chloride, the aqueous phase adjusted to pH5.8 with sodium hydroxide solution and evaporated to dryness in vacuo.The residual solid was dissolved in 10 ml. 95% ethanol and ethyl etheradded to precipitate the title compound in two crops:

1.66 g., [alpha]_(D) +13.4° (C=0.9, 1.2 N HCl), M.P. 85°-90° C.;

1.20 g., [alpha]_(D) +13.9° (C=0.8, 1.2 N HCl).

TLC of each crop showed product spot at R_(f) 0.51 with small amount ofmaterial of R_(f) 0.44.

F. Purification via p-toluenesulfonate salt

To 10 ml. water was added 1.39 g. (3.85 mmole) of the combined crops ofproduct obtained above and 0.66 g. (3.83 mmole) p-toluenesulfonic acid.The resulting solution was stirred at room temperature for two hours.The precipitated solid was collected by filtration and washed with asmall amount of water to afford 0.94 g. of p-toluenesulfonate salt. Thesalt was combined with 3 ml. of liquid anion exchange resin (AmberliteLA-1®), 6 ml. hexane, 2 ml. water and the mixture stirred for two hours.The aqueous phase was separated, washed with hexane and evaporated todryness in vacuo to give 0.72 g. of off-white solid, [alpha]_(D) +22.43°(C=0.8, 1.2 N HCl); R_(f) 0.48.

Sweetness potency: 320×sucrose. The sweet taste was judged to beunusually clean, free of off flavor notes and to have a quick sweetnessimpact.

EXAMPLE 8 L-Aspartyl-D-O-methylserineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide ##STR61##

In 75 ml. methylene chloride was dissolved 3.8 g. (15 mmole)N-benzyloxycarbonyl-D-O-methylserine. N-methylmorpholine (1.68 ml.) wasadded, the solution cooled to -15° C. and 1.43 ml. ethyl chloroformateadded. The resulting mixture was stirred for 8 minutes at -15° C., then2.18 g. (15 mmole) 3-amino-2,2,4,4-tetramethylthietane was added and themixture allowed to warm to room temperature. Stirring was continued fortwo hours at room temperature, the reaction mixture washed with dilutesodium hydroxide, dilute hydrochloric acid, dried (MgSO₄) and thesolvent evaporated in vacuo to give 6.11 g. of liquid product, R_(f)0.58 (ethyl acetate/hexane 1:1; phosphomolybdate spray).

B. Oxidation to 1,1-dioxide

The product from Part A, above, 6.11 g., was dissolved in 75 ml.chloroform and cooled in ice while adding 7.12 g. m-chloroperbenzoicacid in portions. The reaction mixture was allowed to warm to roomtemperature and stirred for three hours. Additional chloroform (75 ml.)was added and the solution washed twice each with 5% (w/v) sodiumcarbonate solution, 0.5 N sodium thiosulfate and 1 N hydrochloric acid.After drying the organic phase (MgSO₄) and evaporation of solvent, 6.24g. of product was obtained as a viscous liquid, R_(f) 0.22 (ethylacetate/hexane, 1:1; phosphomolybdate spray) with traces of startingmaterial and sulfoxide. The ¹ H-NMR spectrum was in agreement with thestructure for the desired sulfone with a small amount of chloroform.##STR62##

A mixture of 6.11 g. of N-benzyloxycarbonyl-D-O-methylserineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, 250 ml. methanol and3.0 g. 5% palladium-on-carbon catalyst was hydrogenated at 50 psi (3.52km./cm.²) for two hours. The catalyst was removed by filtration, thefiltrate was evaporated in vacuo and the residue taken up in 35 ml. 1 Nhydrochloric acid. The acidic solution was washed three times withchloroform, made alkaline with solid sodium hydroxide, saturated withsodium chloride and extracted with 3×50 ml. chloroform. The combinedextracts were dried (MgSO₄) and solvent evaporated in vacuo to give 3.37g. (80%) of the alpha-amino amide product as a colorless liquid, R_(f)0.29; [alpha]_(D) -15.7° (C=0.8, 1 N HCl). The structure was verified by¹ H-NMR spectroscopy. ##STR63##

Employing 3.37 g. (12 mmole) of the product obtained in Part C, above,as starting material, in the procedure of Example 1, Part D, the desireddiblocked dipeptide amide was obtained a clear glass, 6.73 g, (91%),R_(f) 0.28 (ethyl acetate/hexane, 70:30). The ¹ H-NMR spectrum was inagreement with the structure for this compound.

E. A mixture of 6.73 g. beta-benzyl N-Cbz-L-aspartyl-D-O-methylserineN-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide, 250 ml. methanol and2.0 g. 5% Pd/C catalyst was hydrogenated by the procedure of Part C,above. The residue remaining after evaporation of solvent was stirredovernight in ethyl ether and the solid product collected by filtrationand dried in the vacuum oven to yield 3.3 g. (77%) of the desireddipeptide amide, R_(f) 0.23; M.P. 140°-150° C. (dec.); [alpha]_(D)+20.3° (C=1, 1.2 N HCl).

Sweetness potency: 200×sucrose.

EXAMPLE 9 L-Aspartyl-D-serineN-(dl-cis,trans-2,6-dimethylcyclohexyl)amide ##STR64##

A. dl-cis,trans-2,6-Dimethylcyclohexylamine

A solution of 2.1 g. trans-2,6-dimethylcyclohexanone oxime in 30 ml. dryethanol was heated at reflux. To this was added in portions 3.1 g. ofmetallic sodium. When the addition was complete, the mixture wasmaintained at reflux for 30 minutes and allowed to cool to roomtemperature. The resulting gel was dissolved in water, adjusted to pH2.0 with hydrochloric acid and washed with ethyl ether. The aqueousphase was made alkaline with sodium hydroxide, extracted with ether, theextracts dried (MgSO₄) and evaporated to provide the desired amine as acolorless liquid.

B. D-Serine N-(dl-cis,trans-2,6-dimethylcyclohexyl)amide

Employing 1.47 g. (6.15 mmole) N-Cbz-D-serine, 775 mg. (6.15 mmole)dl-cis,trans-2,6-dimethylcyclohexylamine and equimolar amounts ofN-methylmorpholine and ethyl chloroformate and subsequent removal ofamino-protecting group by catalytic hydrogenation by the procedures ofExamples 1, Parts B and C, afforded 0.70 g. of the desired D-serine andamide as a white solid, R_(f) 0.64 (ethyl acetate/hexane, 7:3).

C. Diprotected Dipeptide Amide

By employing 600 mg. (2.8 mmole) ofD-serine-N-(dl-cis,trans-2,6-dimethylcyclohexyl)amide in the procedureof Example 1, Part D, the corresponding beta-benzylN-benzyloxycarbonyl-L-aspartyl-D-serine amide, 1.2 g., was obtained as acolorless solid. Recrystallization from isopropyl ether gave 1.0 g.,R_(f) 0.35 (ethyl acetate/hexane, 7:3).

D. Catalytic hydrogenation of the diprotected dipeptide amide providedin Part C, above, (1.0 g.) in methanol in the presence of 0.6 g. 5%palladium/carbon catalyst by the procedure of Example 1, Part E, yielded435 mg. of the title compound as an off-white crystalline solid.

Sweetness potency: 200×sucrose.

EXAMPLE 10 Beta-Benzyl N-benzyloxycarbonyl-L-Aspartyl-D-O-methylserine##STR65##

D-O-Methylserine (6.65 g., 56.1 mmole) is dissolved in 100 ml. ofN,N-dimethylformamide (DMF) and to the solution is added dropwise atroom temperature 6.74 g. (62.4 mmole) of trimethylchlorosilane. In aseparate flask is placed beta-benzyl N-benzyloxycarbonyl-L-aspartate(18.0 g., 50.4 mmole), triethylamine (12.35 g., 122 mmole) and 110 ml.each of DMF and tetrahydrofuran and the resulting solution cooled to-15° C. To the solution is added ethyl chloroformate (5.95 g., 55.1mmole) and the resulting mixture stirred for ten minutes at -10° C. Tothis is then added dropwise the DMF solution of silylatedD-O-methylserine prepared above while maintaining the mixture at -5° to-10° C. The mixture is stirred at -5° C. for one hour, 0.2 Nhydrochloric acid added until the mixture is acidic and the resultingmixture extracted with chloroform. The chloroform extracts are combinedand washed several times with dilute hydrochloric acid to removeremaining DMF. The solvent is evaporated in vacuo to provide the titlecompound.

When the procedure is repeated, but employing D-serine in place ofD-O-methylserine and twice the above amount of trimethylchlorosilane,beta-benzyl N-Cbz-L-aspartyl-D-serine is obtained in like manner.

EXAMPLE 11 Beta-Methyl-N-benzyloxycarbonyl-L-aspartyl-D-serine

A suspension of 80.7 g. (0.78 mole) D-serine in 200 ml. of DMF is cooledto 10° C., 184 g. (1.70 mole) of trimethylchlorosilane is added inportions and the resulting mixture stirred at 25° C. for one hour.

In a separate flask is placed a solution of 158 g. (0.86 mole) ofbeta-methyl L-aspartic acid hydrochloride in one liter of water. To thisis added 34.5 g. (0.86 mole) of sodium hydroxide followed by 80 g. ofsodium bicarbonate and the resulting mixture stirred vigorously. Aftercooling to 5°-10° C. 161 g. (0.94 mole) of benzyloxycarbonyl chloride isadded in portions and stirring continued for two hours at thistemperature. The reaction mixure is washed with 100 ml. of ethylacetate, acidified by addition of 80 ml. of concentrated hydrochloricacid and extracted with ethyl acetate (2×450 ml.). The extract (900 ml.)is found to contain 218 g. (0.78 mole, 90% yield) ofbeta-methyl-N-benzyloxycarbonyl-L-aspartate. It is used in the next stepwithout further purification.

The ethyl acetate extract is cooled to -20° C., 165 g. (1.63 mole) oftriethylamine and 84 g. (0.78 mole) ethyl chloroformate are added. Thesolution is stirred at -15° to -20° C. for 30 minutes then treatedquickly with the DMF solution of silylated D-serine prepared above andthe resulting mixture is allowed to warm to ambient temperature over onehour with stirring. The reaction mixture is washed with water (3×500ml.), the organic layer dried over sodium sulfate and evaporated invacuo to afford the title compound.

When the procedure is repeated, but employing D-O-methylserine in placeof D-serine and only half the above amount of trimethylchlorosilane,beta-methyl N-Cbz-L-aspartyl-D-O-methylserine is obtained.

By use of DL-serine or DL-O-methylserine in the procedures of Examples10 and 11 the corresponding diblocked L-aspartyl-DL-amino aciddipeptides of the formula below are obtained. ##STR66## where Cbz isOCOCH₂ C₆ H₅, R^(b) is H or CH₃ and R¹⁰ is CH₃ or CH₂ C₆ H₅.

EXAMPLE 12 L-Aspartyl-D-serine N-(trans-2-methylcyclohexyl)amide

A. To a solution of 228 g. (0.62 mole) ofbeta-methyl-N-benzyloxycarbonyl-L-aspartyl-D-serine in one liter ofethyl acetate is added 69 g. (0.68 mole) triethylamine, the mixture iscooled to -20° C. and 67 g. (0.62 mole) of ethyl chloroformate is added.The resulting solution is stirred for 30 minutes at -15° to -20° C.,then treated with 76.5 g. (0.68 mole) of trans-2-methylcyclohexylamineand stirring continued for 30 minutes. After allowing to warm to roomtemperature the mixture is washed twice with 500 ml. portions of watercontaining 15 ml. of concentrated hydrochloric acid, twice with 500 ml.of 5% aqueous sodium bicarbonate, then water. The organic layer is dried(Na₂ SO₄), concentrated in vacuo to about 200 ml. and 400 ml. of hexanewas added whereupon beta-methyl-N-benzyloxycarbonyl-L-aspartyl-D-serineN-(trans-2-methylcyclohexyl)amide precipitated.

B. To 230 g. (0.50 mole) of the product obtained in Part A, above,dissolved in 500 ml. of methanol is added a solution of 24 g. (0.60mole) of sodium hydroxide in 500 ml. of water. The mixture is stirred at30° C. for one hour, neutralized to about pH 7 with dilute hydrochloricacid and charged into an autoclave. Two grams of 5% palladium/carboncatalyst is added and the mixture hydrogenated at 25° C., 3.5 kg./cm.²(50 psi) for one hour. The catalyst is removed by filtration, thefiltrate evaporated in vacuo to 200 ml., the concentrate acidified to pH5.2 with concentrated hydrochloric acid, then granulated at 5° C. forone hour. The resulting precipitate is collected by filtration, the wetcake dissolved in a mixture of water and concentrated hydrochloric acid,carbon treated, filtered and the filtrate adjusted to pH 5.2 with 50%(w/w) sodium hydroxide solution. After granulation at 5° C., filtering,washing with cold water and drying, the desired product is obtained.

By employing the appropriate beta-methyl-N-Cbz-L-aspartyl-D (orDL)-amino acid dipeptide in the above procedures the correspondingdipeptide amides of the formula below, where R^(a) is CH₂ OH or CH₂OCH₃, are obtained in like manner. ##STR67##

EXAMPLE 13 L-Aspartyl-D-O-methylserineN-(dl-t-butylcyclopropylcarbinyl)amide: ##STR68##

A. t-Butylcyclopropylcarbinylamine

To 0.5 mole each of cyclopropanecarbonyl chloride and cuprous chloridein 500 ml. of dry ethyl ether was added dropwise under a nitrogenatmosphere 238 ml. (0.5 mole) of 2.1 M t-butylmagnesium chloride in thesame solvent at -10° C. The reaction mixture was poured into a mixtureof 250 ml. of 3 M hydrochloric acid and 700 g. of ice, the organic layerseparated, washed with water, sodium bicarbonate solution, brine anddried over anhydrous magnesium sulfate. The ether was evaporated atreduced pressure and the residue distilled at atmospheric pressure toprovide 45 g. (72%) of t-butylcyclopropylketone, B.P. 145°-153° C.

The 45 g. (0.36 mole) of ketone was reacted with hydroxylaminehydrochloride and sodium acetate in 1:1 ethanol/water by the method ofPreparation Q. After heating at reflux overnight the reaction mixturewas cooled and the precipitated oxime collected and washed with coldethanol to obtain 23.5 g. of t-butylcyclopropylketoxime. An additional7.7 g. was obtained from the mother liquors. The combined crops wererecrystallized from 1:1 ethanol/water to provide 25.2 g. (50%) of oxime,M.P. 113.5°-114° C.

To a solution of 5.0 g. (0.035 mole) of oxime in 80 ml. of ethanol wasadded 8.04 g. (0.35 mole) of sodium and the reaction carried out andproduct isolated as described in Preparation Q, to afford 3.31 g. ofcrude dl-t-butylcyclopropylcarbinylamine. This was distilled atatmospheric pressure to yield 2.01 g. (45%) of product boiling at153°-155° C. ##STR69##

To a 250 ml. three-necked flask fitted with a stopper, thermometer,drying tube and magnetic stirring bar was added 2.82 g. (6.6 mmole) ofbeta-benzyl-N-benzyloxycarbonyl-L-aspartyl-D-O-methylserine, 50 ml.tetrahydrofuran and 1.0 ml. (7.0 mmole) triethylamine. The mixture wascooled to -10° C., 0.69 ml. (7.0 mmole) ethyl chloroformate was added,stirred for 20 minutes, cooled to -35° C. and 0.76 g. (0.66 mmole) ofdl-t-butylcyclopropylcarbinylamine added. The reaction mixture wasallowed to warm slowly to room temperature and stirred overnight. Themixture was poured into 100 ml. water, extracted with 170 ml. of ethylacetate and the organic phase washed with 5% aqueous sodium bicarbonate(2×50 ml.), 3 M hydrochloric acid (2×50 ml.), brine (1×70 ml.) and driedover anhydrous magnesium sulfate. The dried extract was evaporated todryness in vacuo to provide the crude diblocked dipeptide amide whichwas purified by column chromatography on silica gel.

C. The purified product from Part B, 2.33 g., was hydrogenated over apalladium-on-carbon catalyst as described in Example 1, Part E, toafford the desired dipeptide amide.

The compound of formula (I) wherein R is ##STR70## and R^(a) is CH₂ OHis similarly obtained from the appropriate diblocked dipeptide.

EXAMPLE 14

By employing the appropriate amine of formula RNH₂ in the procedure ofthe preceding Examples the following L-aspartyl-D-amino acid amides areprovided in like manner.

    ______________________________________                                         ##STR71##                                                                    where R.sup.a is CH.sub.2 OH:                                                   R                 R                                                         ______________________________________                                        2,5-dimethylcyclopentyl,                                                                        2,6-diisopropylcyclohexyl,                                  2,5-diethylcyclopentyl,                                                                         2,2-dimethylcyclohexyl,                                     2,5-diisopropylcyclopentyl,                                                                     2,2,6-trimethylcyclohexyl,                                  2-methyl-5-isopropylcyclo-                                                                      2,2,6,6-tetramethylcyclo-                                   pentyl,           hexyl,                                                      2,2,5-trimethylcyclopentyl,                                                                     1-fenchyl,                                                  trans-2-ethylcyclohexyl,                                                                        d1-fenchyl,                                                 trans,trans-2-methyl-5-                                                                         2-methylcyclopentyl,                                        ethylcyclohexyl,  2-ethylcyclopentyl,                                         2,2,5,5-tetramethylcyclo-                                                                       2-isopropylcyclopentyl,                                     pentyl            2-t-butylcyclopentyl,                                       2,2,4,4-tetramethyltetra-                                                                       t-butylcyclopentylcarbinyl,                                 hydrofuran-3-yl,  diisopropylcarbinyl,                                        2-methyl-6-ethylcyclohexyl,                                                                     d-methyl-t-butylcarbinyl,                                   2,6-diethylcyclohexyl,                                                                          d1-methyl-t-butylcarbinyl,                                  2-isopropylcyclohexyl,                                                                          di-t-butylcarbinyl,                                         2-t-butylcyclohexyl,                                                                            isopropyl-t-butylcarbinyl,                                  2-methyl-6-t-butylcyclohexyl,                                                                   methyl-isobutylcarbinyl,                                    dicyclobutylcarbinyl,                                                                           2,2,3,3-tetramethylcyclo-                                   dicyclopentylcarbinyl,                                                                          propyl,                                                     dicyclohexylcarbinyl,                                                                           2,2,4,4-tetramethylcyclobutyl,                              dicycloheptylcarbinyl,                                                                          2-methyloxetan-3-yl,                                        cyclobutylcyclopropyl-                                                                          2,2-dimethyloxetan-3-yl                                     carbinyl          2-t-butyl-4-methyloxetan-3-                                 cyclobutylcycloheptyl-                                                                          yl,                                                         carbinyl          2,4-diethyl-2,4-dimethyl-                                   cyclopentylcyclopropyl-                                                                         oxetan-3-yl,                                                carbinyl          2,4-dimethyloxetan-3-yl,                                    2,2,4,4-tetramethyl-3-oxo-                                                                      2,2-diethyl-4,4-dimethyl-                                   cyclobutyl        oxetan-3-yl,                                                2,2,4,4-tetramethyl-3-                                                                          2-sec-butylcyclopentyl,                                     hydroxycyclobutyl,                                                                              2-2-di-n-propylcyclopentyl,                                 2-methylcyclobutyl,                                                                             2,4-dimethyltetrahydrofuran-                                2,4-dimethylcyclobutyl,                                                                         3-yl,                                                       2,2-dimethyl-4-ethylcyclo-                                                                      2-methyltetrahydrofuran-3-yl,                               butyl,            2-t-butyltetrahydrofuran-3-                                 2,2,4,4-tetramethylcyclo-                                                                       yl,                                                         butyl             2-ethyl-4-n-butyltetrahydro-                                2,2-diethyl-4,4-dimethyl-                                                                       furan-3-yl,                                                 cyclobutyl,       2-n-butyl-4-ethyltetrahydro-                                2,4-diisopropylcyclobutyl,                                                                      furan-3-yl,                                                 2-t-butylcyclobutyl,                                                                            3,5-dimethyltetrahydropyran-                                2-methylcycloheptyl,                                                                            4-yl,                                                       2-isopropylcyloheptyl,                                                                          3,5-diisopropyltetrahydro-                                  2-t-butylcycloheptyl,                                                                           pyran-4-yl,                                                 2,7-dimethylcycloheptyl,                                                                        3,3,5,5-tetramethyltetra-                                   2,7-diisopropylcycloheptyl,                                                                     hydropyran-4-yl                                             3-t-butyl-5-methyltetrahydro-                                                                   2,2,4,4-tetrahydropyran-3-yl,                               pyran-4-yl        4,4-dimethyltetrahydropyran-                                2-methyltetrahydropyran-3-yl,                                                                   3-yl,                                                       4-methyltetrahydropyran-3-yl,                                                                   2,2,5,5-tetramethyl-3-cyclo-                                4-sec-butyltetrahydropyran-                                                                     pentenyl,                                                   3-yl,             2,5-dimethyl-3-cyclopentenyl,                               2-isopropyltetrahydropyran-                                                                     2-methyl-3-cyclopentenyl,                                   3-yl,             2,5-diisopropyl-3-cyclo-                                    2,4-diisopropyltetrahydro-                                                                      pentenyl,                                                   pyran-3-yl,       4-methyloxepane-3-yl,                                       2-methyloxepane-3-yl,                                                                           2,2,4,4-tetramethyloxepane-                                 2,4-dimethyloxepane-3-yl,                                                                       3-yl,                                                       2,4-diisopropyloxepane-3-yl,                                                                    2,2-dimethyloxepane-3-yl,                                   3-methyloxepane-4-yl,                                                                           5,5-dimethyloxepane-4-yl,                                   3,3-dimethyloxepane-4-yl,                                                                       3-isopropyloxepane-4-yl,                                    3,5-diisopropyloxepane-4-yl,                                                                    2,4-dimethyltetrahydropyran-                                5-isopropyloxepane-4-yl,                                                                        3-yl,                                                       2-isopropylclyclopropyl,                                                                        2-t-butylcyclopropyl,                                       2,2-dimethylcyclopropyl,                                                                        ethylcyclopropylcarbinyl,                                   isopropylcyclopropylcarbinyl                                                  ______________________________________                                    

where R^(a) is CH₂ OCH₃ :

    ______________________________________                                           R                                                                          ______________________________________                                        2,2-dimethyl-5-t-butylcyclopentyl, -2-isobutylcyclohexyl,                     2-n-butyl-6-ethylcyclohexyl,                                                  2,2-diethylcyclohexyl,                                                        2-t-butyl-6-methylcyclohexyl,                                                 2,4-diethyl-2,4-dimethyltetrahydrofuran-3-yl,                                 2,4-dimethyltetrahydrofuran-3-yl,                                             2,2,4,4-tetramethyltetrahydrofuran-3-yl,                                      3,5-dimethyltetrahydropyran-4-yl,                                             3,3,5,5-tetramethyltetrahydropyran-4-yl,                                      2,2,4,4-tetramethyltetrahydropyran-3-yl,                                      4,4-dimethyltetrahydropyran-3-yl,                                             2,2-dimethyltetrahydropyran-3-yl,                                             3,3,5,5-tetramethyloxepane-4-yl,                                              2,3-diisopropylcyclopropyl,                                                   2-t-butylcyclopropyl,                                                         isopropylcyclopropylcarbinyl,                                                 d-methyl-t-butylcarbinyl,                                                     diisopropylcarbinyl,                                                          di-t-butylcarbinyl,                                                           l-fenchyl,                                                                    2,2,5-trimethyl-3-cyclopentenyl.                                              ______________________________________                                    

    ______________________________________                                        R            R             R                                                  ______________________________________                                         ##STR72##                                                                                  ##STR73##                                                                                   ##STR74##                                          ##STR75##                                                                                  ##STR76##                                                                                   ##STR77##                                          ##STR78##                                                                                  ##STR79##                                                                                   ##STR80##                                          ##STR81##                                                                                  ##STR82##                                                                                   ##STR83##                                          ##STR84##                                                                                  ##STR85##                                                                                   ##STR86##                                          ##STR87##                                                                                  ##STR88##                                                                                   ##STR89##                                          ##STR90##                                                                                  ##STR91##                                                                                   ##STR92##                                          ##STR93##                                                                                  ##STR94##                                                                                   ##STR95##                                          ##STR96##                                                                                  ##STR97##                                                                                   ##STR98##                                          ##STR99##                                                                                  ##STR100##                                                                                  ##STR101##                                         ##STR102##                                                                                 ##STR103##                                                                                  ##STR104##                                         ##STR105##                                                                                 ##STR106##                                                                                  ##STR107##                                         ##STR108##                                                                                 ##STR109##                                                                                  ##STR110##                                         ##STR111##                                                                                 ##STR112##                                                                                  ##STR113##                                        ______________________________________                                    

EXAMPLE 15 L-Aspartyl-D-O-methylserineN-(3,5-dimethyltetrahydrothiopyran-4-yl)amide: ##STR114## mixture ofcis/trans and trans/trans isomers

A. 3,5-Dimethyltetrahydrothiopyran-4-one

A mixture of 2 g. of sodium acetate and 25 ml. of ethanol was saturatedwith hydrogen sulfide gas. To this was added 7.0 g. (0.063 mole)diisopropenylketone while cooling in an ice bath until the reaction wasno longer exothermic. The mixture was stirred at room temperature whilepassing hydrogen sulfide through the mixture for four hours then allowedto stand overnight. The ethanol and excess H₂ S were evaporated in vacuoand the residue taken up in ethyl ether, washed in turn with water,potassium carbonate solution, dilute hydrochloric acid, and water again.The ether extracts were dried (Na₂ SO₄) and evaporated to provide 6.8 g.of oil. This was distilled in vacuo through a 10 cm. Vigreaux column toprovide 1.67 g. of product, B.P. 83°-86° C./9 mm. which was used in thenext step without further purification.

B. 4-Oximino-3,5-dimethyltetrahydrothiopyran

A mixture of 1.67 g. (0.011 mole) of the cyclic ketone obtained in PartA, 1.6 g. (0.023 mole) hydroxylamine hydrochloride and 1.9 g. (0.023mole) sodium acetate in 30 ml. of water and 10 ml. of ethanol wereheated at reflux for three hours, cooled and the precipitate recoveredby filtration. After recrystallization from 1:1 methanol-water 1.5 g. ofoxime was obtained as a white solid, M.P. 60°-85° C. which is a mixtureof isomers of suitable purity for use in the next step.

C. trans/trans and cis/trans-4-Amino-3,5-dimethyltetrahydrothiopyran

To a solution of 1.45 g. (0.009 mole) of the oxime obtained in Part B in15 ml. of ethanol was added in portions 5 g. of sodium shot followed byan additional 25 ml. of ethanol and the resulting mixture heated atreflux for about 30 minutes. The reaction mixture was diluted withwater, extracted with ethyl ether, and the extracts washed with water.The ether layer was extracted with dilute hydrochloric acid and theaqueous layer washed with fresh ether. The aqueous layer was madealkaline by addition of sodium hydroxide solution and extracted withether again. The organic layer was dried (MgSO₄) and the etherevaporated to obtain 1.1 g. of residual colorless oil. Gas-liquidchromatography (OV-1 column with temperature programming from 80° to100° C.) showed the product to contain two major components in a 60/40ratio. ¹ H-NMR (CDCl₃) indicated the product to be a mixture of4-amino-3-trans-5-trans-dimethyltetrahydrothiopyran and thecorresponding 3-cis-5-trans-isomer.

D.N(3,5-Dimethyltetrahydrothiopyran-4-yl)-t-butoxycarbonyl-D-O-methylserineamide##STR115##

Under anhydrous conditions, to a mixture of 1.96 g. (8.9 mmole) ofN-t-Boc-D-O-methylserine obtained in Example 7, Part A, 1.98 g. (19mmole) triethylamine and 40 ml. of tetrahydrofuran, cooled to -10° C.,is added dropwise 0.96 g. (8.9 mmole) ethyl chloroformate and theresulting mixture stirred at this temperature for 20 minutes. To this isadded 1.1 g. (7.5 mmole) of the mixture of isomers of4-amino-3,5-dimethyltetrahydrothiopyran obtained in Part C and theresulting mixture stirred at -10° C. for 10 minutes then allowed to warmto room temperature. The reaction mixture is diluted with water andextracted with ethyl acetate. The organic layer is washed with sodiumbicarbonate solution, dilute hydrochloric acid, water, brine then dried(Na₂ SO₄) and the solvent evaporated at reduced pressure to obtain theproduct.

E. N-(3,5-Dimethyltetrahydrothiopyran-4-yl)-D-O-methylserine amide##STR116##

The t-Boc-amide obtained in Part D is dissolved in 15 ml. of ethanol anda mixture of 5 ml. of concentrated hydrochloric acid and 10 ml. of waterare added. The resulting mixture is heated at reflux for 30 minutes,cooled and the ethanol removed by evaporation in vacuo. The aqueousresidue is washed with ethyl ether, made alkaline with sodium hydroxidesolution, extracted with ether and the extracts dried (Na₂ SO₄).Evaporation of solvent provides the desired amino amide.

F. Coupling of D-O-methylserine amide with L-aspartic acidN-thiocarboxyanhydride

The D-O-methylserine amide provided in Part E, 1.25 g. (5.1 mmole) isdissolved in 5 ml. of tetrahyrofuran and 5 ml. of water was added. Theclear solution is cooled in ice and 0.89 g. (5.1 mmole) of L-asparticacid N-thiocarboxyanhydride is added in one portion. To this is added asrequired, 0.5 M sodium hydroxide to maintain the mixture of pH 9. Afterstirring 30 minutes the reaction mixture is washed with ethyl ether thenethyl acetate and the washes discarded. The aqueous phase is acidifiedwith dilute hydrochloric acid to pH 5.6 and evaporated to dryness atreduced pressure. The residue is taken up in hot methanol (100 ml.),filtered and the methanol evaporated. The residue was taken up again inhot methanol, filtered and the filtrate decolorized with activatedcarbon, filtered through diatomaceous earth and the filtrate evaporatedto obtain the crude product. The crude product is dissolved in hot water(11 ml.) and filtered, evaporated under a stream of nitrogen to 5 ml.and cooled in ice to precipitate the product which is collected byfiltration and dried.

Use of t-Boc-D-serine, t-Boc-DL-serine or t-Boc-DL-O-methylserine inplace of t-Boc-D-O-methylserine in the procedure of Part D, above, andreacting the resulting N-t-Boc-D (or DL)-amino acid in the procedures ofParts D, E and F, provides the corresponding compounds of formula (I)wherein R is 3,5-dimethyltetrahydrothiopyran-4-yl and R^(a) is CH₂ OH orCH₂ OCH₃.

EXAMPLE 16 L-Aspartyl-D-serineN-(2,2,4,4-tetramethyltetrahydrothiophene-3-yl)amide: ##STR117##

To a solution of 2.26 g. (11 mmole) of N-t-butoxycarbonyl-D-serine in 75ml. of tetrahydrofuran is added 1.47 ml. (10 mmole) of triethylamine andthe mixture cooled to -10° C. At this temperature is added 0.96 ml. (10mmole) of ethyl chloroformate and stirring continued for 15 minutes.After cooling to -20° C., 1.6 g. (10 mmole) ofdl-3-amino-2,2,4,4-tetramethyltetrahydrothiophene is added and theresulting mixture is allowed to warm to room temperature. Ethyl acetateis added and the mixture is washed twice with 50 ml. portions of 5% (byweight) aqueous citric acid, aqueous sodium bicarbonate (1×50 ml.) andsaturated brine (1×50 ml.). The organic layer is dried (Na₂ SO₄) andevaporated to dryness at reduced pressure to affordN(2,2,4,4-tetramethyltetrahydrothiophene-3-yl)-t-butoxycarbonyl-D-serineamide. This product is used without further purification in the nextstep. ##STR118##

To 3 g. of the product from Part A is added 5 ml. of methanol and 30 ml.of 1 M hydrochloric acid and the mixture is heated on the steam-bath for30 minutes. The methanol is removed by evaporation and the residueextracted with ether. The ether is discarded and the aqueous phase isadjusted to pH 11.0 with sodium hydroxide solution, extracted with ethylacetate, the extracts dried (Na₂ SO₄) and evaporated to dryness toobtain D-serine N(2,2,4,4-tetramethyltetrahydrothiophene-3-yl)-amide.

C. Coupling to form dipeptide amide

The D-serine amide obtained in Part B, 1.03 g. (4.25 mmole) is mixedwith 10 ml. of water, cooled in ice and the pH of the mixture adjustedto 9.2 with 0.5 N sodium hydroxide solution. To this is addedportionwise with stirring 0.8 g. (4.25 mmole) of L-aspartic acidN-thiocarboxyanhydride while maintaining the mixture at pH 9 with sodiumhydroxide solution (0.5 N). When the addition is completed the resultingmixture is stirred at 0° C. for 45 minutes, adjusted to pH 5.2 withhydrochloric acid and evaporated to dryness in vacuo. The residue isslurried with methanol, filtered to remove precipitated solids andmethanol removed from the filtrate by evaporation at reduced pressure.The resulting crude product is purified by column chromatography onsilica gel.

EXAMPLE 17

Employing the procedures of Examples 3, 7, 8, 15 and 16, correspondingL-aspartyl-D-amino acid amides (I) wherein R^(a) is CH₂ OH or CH₂ OCH₃and R is as defined below are prepared from the appropriate startingmaterials via D-R^(a) CH(NH₂)CONHR intermediates. The correspondingL-aspartyl-DL-amino acid amides are similarly provided when at-Boc-DL-amino acid is employed in place of the D-enantiomer. Likewise,use of DL-aspartic N-thiocarboxyanhydride in the coupling step affordsthe DL-D or DL-DL compounds of formula (I).

    ______________________________________                                         ##STR119##                                                                   R           R              R                                                  ______________________________________                                         ##STR120##                                                                                ##STR121##                                                                                   ##STR122##                                         ##STR123##                                                                                ##STR124##                                                                                   ##STR125##                                         ##STR126##                                                                                ##STR127##                                                                                   ##STR128##                                         ##STR129##                                                                                ##STR130##                                                                                   ##STR131##                                         ##STR132##                                                                                ##STR133##                                                                                   ##STR134##                                         ##STR135##                                                                                ##STR136##                                                                                   ##STR137##                                         ##STR138##                                                                                ##STR139##                                                                                   ##STR140##                                         ##STR141##                                                                                ##STR142##                                                                                   ##STR143##                                         ##STR144##                                                                                ##STR145##                                                                                   ##STR146##                                         ##STR147##                                                                                ##STR148##                                                                                   ##STR149##                                         ##STR150##                                                                                ##STR151##                                                                                   ##STR152##                                         ##STR153##                                                                                ##STR154##                                                                                   ##STR155##                                         ##STR156##                                                                                ##STR157##                                                                                   ##STR158##                                         ##STR159##                                                                                ##STR160##                                                                                   ##STR161##                                         ##STR162##                                                                                ##STR163##                                                                                   ##STR164##                                         ##STR165##                                                                                ##STR166##                                                                                   ##STR167##                                         ##STR168##                                                                                ##STR169##                                                                                   ##STR170##                                         ##STR171##                                                                                ##STR172##                                                                                   ##STR173##                                         ##STR174##                                                                                ##STR175##                                                                                   ##STR176##                                         ##STR177##                                                                   ______________________________________                                    

EXAMPLE 18 L-Aspartyl-D-serineN-(2-methylthio-2,4-dimethylpentan-3-yl)amide

A. 2-Methylthio-2,4-dimethylpentan-3-one

A solution of 200 ml. of methanol containing 9.2 g. (0.40 mole) sodiummetal was cooled in an ice-bath and saturated with gaseous methylmercaptan. To this was added 77.2 g. (0.40 mole) of2-bromo-2,4-dimethylpentan-3-one at room temperature and the resultingmixture stirred for two hours. The reaction mixture was diluted withwater, extracted with ethyl ether, the extracts washed with water, brineand dried over anhydrous sodium sulfate. The ether was evaporated andthe residue distilled in vacuo to afford 50.4 g. of product, B.P. 76°(20 mm.).

B. 2-Methylthio-2,4-dimethyl-3-aminopentane

A solution of 6.0 g. (0.038 mole) 2-methylthio-2,4-dimethylpentan-3-one,9.9 g. formamide and 2.1 g. of 100% formic acid was heated at refluxwhile removing water formed in the reaction by means of a fractionatinghead. After 12 hours an additional 2.5 g. of formic acid was added andreflux continued for another 24 hours in the same manner, by which timethe reaction mixture reached a temperature of 190° C. The mixture wascooled, diluted with water and extracted with ethyl acetate. Theextracts were washed with water and evaporated to dryness at reducedpressure to provide 5.3 g. of residual oil. The oil was refluxed with 40ml. of 6 N hydrochloric acid for six hours, diluted with water, washedwith ether and the aqueous phase made strongly alkaline with sodiumhydroxide. After extracting with ethyl ether and evaporation of theextract, 3.3 g. (56%) of colorless amine was obtained which gave asingle peak by gas-liquid chromatography on a six foot OV-1 column at110° C.; retention time 412 seconds.

C. D-Serine N-(2-methylthio-2,4-dimethylpentan-3-yl)amide

To a solution of 3.47 g. (0.017 mole) N-t-butoxycarbonyl-D-serine and2.5 g. (0.017 mole) triethylamine in 100 ml. of tetrahydrofuran at -15°C. is added 1.63 ml. of ethyl chloroformate. After stirring for 15minutes, 2.49 g. (0.017 mole) 2-methylthio-2,4-dimethyl-3-aminopentaneis added and the mixture stirred for one hour. The reaction mixture isdiluted with ethyl acetate, washed with water, 5% aqueous citric acid(w/v), sodium bicarbonate solution and brine. The organic phase isevaporated to dryness. The residue is taken up in 100 ml. methanol, 60ml. of concentrated hydrochloric acid added and the mixture refluxed forone hour. After evaporation of methanol, the residue is taken up inwater, washed with ether, the aqueous phase adjusted to pH 12 withsodium hydroxide and extracted with ethyl ether. Evaporation of theextracts affords the desired D-serine amide.

D. A solution of 3.3 g. (0.013 mole) of the D-serine amide, obtained inPart C, in 30 ml. acetone and 17 ml. water is adjusted to pH 9.9 withsodium hydroxide solution and cooled to -2° C. To this is added 2.78 g.(0.013 mole) L-aspartic N-thiocarboxyanhydride in small portions over 20minutes while maintaining the pH at 9.9 with 1 N sodium hydroxide. Whenthe addition is completed, the resulting mixture is stirred for 30minutes at -2° C., washed with ethyl acetate acidified to pH 2 withhydrochloric acid and washed again with ethyl acetate. The aqueous phaseis then adjusted to pH 5.2 and evaporated to dryness. The crudedipeptide amide is obtained by slurrying the residue in methanol,filtering, treatment of the filtrate with ether and filtering to obtaina second crop.

The crude product is purified by preparative layer chromatography onsilica gel plates (20×20×2 mm.) eluting with butanol/water/acetic acid,4:1:1 by volume. The product zone was cut out and eluted with methanolto give the purified L-aspartyl-D-serine amide.

When N-t-butoxycarbonyl-D-O-methylserine is employed in the procedure ofPart C, above, in place of the N-t-Boc-D-serine used therein, and theresulting product treated by the procedure of Part D, above, thecorresponding L-aspartyl-D-O-methylserine amide is obtained.

EXAMPLE 19 L-Aspartyl-D-serine N-(2-hydroxy-2,4-dimethyl-3-pentyl)amide,##STR178##

A. 2-Hydroxy-2,4-dimethyl-3-pentanone

To a stirred solution of 28.3 ml. (0.2 mole) 2,4-dimethyl-3-pentanone in100 ml. chloroform was added dropwise 10.3 ml. (0.2 mole) bromine in 30ml. of the same solvent. The resulting mixture was stirred for a fewminutes, the solvent evaporated in vacuo, the residue taken up in 100ml. ethanol. Water, 50 ml., and 10 M sodium hydroxide, 50 ml., added.The resulting mixture was stirred at reflux for one hour, diluted with200 ml. water and extracted with 3×50 ml. ethyl ether. The extracts weredried (MgSO₄) evaporated to dryness and the residue distilled to obtain15.95 g. (61%) of the hydroxy-ketone, b.p. 60°-62° C./18 mm.

B. 3-Amino-2-hydroxy-2,4-dimethylpentane

The hydroxy ketone from Part A, 15 g. (0.115 mole) was reduced inrefluxing mixture of formamide and formic acid by the method of Example13, Part D, to obtain 4.5 g. (30%) of the hydroxy amine, b.p. 80°-81°C./17 mm.

C. Diblocked dipeptide amide

To a solution of 2.22 g. (5.0 mmole)betabenzyl-N-benzyloxycarbonyl-L-aspartyl-D-serine in 35 ml.tetrahydrofuran cooled to -15° C. is added 0.55 ml. (5.0 mmole)N-methylmorpholine and 0.48 ml. (5.0 mmole) ethyl chloroformate. Themixture is stirred at -15° to -10° C. for two minutes and 0.66 g. (5.0mmole) 3-amino-2-hydroxy-2,4-dimethylpentane is added. The mixture isallowed to warm to room temperature, stirred overnight and worked-up asdescribed in Example 13, Part B, to obtain the diprotected dipeptideamide which is used directly in the next step.

D. The product from Part C, above, in 250 ml. methanol is hydrogenatedover 1.0 g. 5% Pd/C at 60 psi (17 kg./cm.²) for two hours. The catalystis removed by filtration and the solvent evaporated in vacuo. Theresidue is dissolved in methanol and ethyl ether is slowly added withstirring to precipitate the title compound which is collected byfiltration, and dried in vacuo.

EXAMPLE 20 L-Aspartyl-D-O-methylserineN-(DL-2-amino-3,3-dimethyl-4-hydroxybutanoic acid lactone)amide,##STR179##

A. DL-2-Amino-3,3-dimethyl-4-hydroxybutyric acid lactone hydrochloride

Prepared by the method of Wieland, Chem. Ber., 81, 323 (1948):

2-Keto-3,3-dimethyl-4-hydroxybutyric acid lactone, 3.5 g. wasneutralized with dilute sodium hydroxide and the aqueous solutionevaporated to dryness in vacuo. The residue was taken up in 100 ml. warmethanol, filtered hot and a solution of 700 mg. sodium metal in 10 ml.ethanol containing 2 g. hydroxylamine hydrochloride was added. Thesodium salt of 3,3-dimethyl-4-hydroxy-2-oximinobutyric acid lactone, 5g. precipitated and was recrystallized from methanol. the oxime wasformed by decomposition of the sodium salt in 2 N hydrochloric acid,from which it slowly crystallized. After recrystallization frombenzenehexane, M.P. 160° C.

A solution of 25 g. of the oxime in 100 ml. ethanol was added inportions to 5 g. platinum oxide suspended in 150 ml. 2 N hydrochloricacid and the mixture hydrogenated at atmospheric pressure for 2 days.The catalyst was filtered off, the filtrate evaporated and the residuetaken up in 150 ml. ethanol. Treatment with 500 ml. ethyl etherprecipitated DL-2-amino-3,3-dimethyl-4-hydroxybutyric acid lactonehydrochloride, 22 g., which was recrystallized from ethanol/ether, M.P.208°-212° C.

B. Diblocked dipeptide amide

The aminolactone hydrochloride from Part A, 1.65 g. (0.010 mole) in 10ml. methylene chloride and an aquimolar amount of triethylamine isemployed in the procedure of Example 13, Part B, to provide ##STR180##

C. The product from Part B, above, (2.5 g.) is dissolved in 200 ml.methanol, 0.2 g. of 5% Pd/C catalyst added, the mixture hydrogenated andthe product isolated as described in Example 13, Part C, to afford thedesired dipeptide amide.

EXAMPLE 21 L-Aspartyl-D-serineN-(2,2,4,4-tetramethyl-3-hydroxycyclobutyl)amide, ##STR181##

N-Benzyloxycarbonyl-D-serine (0.1 mole), is reacted with cis/trans2,2,4,4-tetramethyl-3-hydroxycyclobutylamine by the method of Example 8,Part A, to provide the N-Cbz-serine amide.

B. Hydrogenation of N-Cbz-serine amide by the method of Example 8, PartC provides the corresponding 2-amino compound, D-serineN-(2,2,4,4-tetramethyl-3-hydroxycyclobutyl)amide. The latter compound isconverted to the title compound by the procedures of Example 8, Parts Dand E.

The corresponding L-aspartyl-D-O-methylserine amide is obtained in likemanner.

EXAMPLE 22 L-Aspartyl-D-serineN-(2,2,4,4-tetramethyl-3-oxocyclobutyl)amide ##STR182##

N-Benzyloxycarbonyl-D-serineN-(2,2,4,4-tetramethyl-3-hydroxycyclobutyl)amide prepared in Example 21,Part A, 36.4 g., (0.10 mole) dissolved in 1500 ml. acetone is cooled to-10° C. under a dry nitrogen atmosphere and 42 ml. (0.11 mole) 2.67 Mchromic anhydride in diluted sulfuric acid is added. After stirring for15 minutes at -10° C., the solvent is evaporated in vacuo, the residuepoured into an ice-water mixture, neutralized with sodium hydroxidesolution and extracted with ethyl ether. The ether extracts are dried(MgSO₄) and evaporated to dryness to obtain the crude product which maybe purified, if desired, by column chromatography on silica gel.

B. Hydrogenation of the product of Part A, above, by the method ofExample 8, Part C provides D-serineN-(2,2,4,4-tetramethyl-3-oxocyclobutyl)amide. This is, in turn,converted to the title compound by the methods described in Example 8,Parts D and E.

EXAMPLE 23

Employing the appropriate amine of formula RNH₂ in the above proceduresthe compounds of formula (I) below, where R^(a) is CH₂ OH or CH₂ OCH₃,are similarly prepared

    ______________________________________                                         ##STR183##                    (I)                                            R                  R                                                          ______________________________________                                         ##STR184##                                                                                       ##STR185##                                                 ##STR186##                                                                                       ##STR187##                                                 ##STR188##                                                                                       ##STR189##                                                 ##STR190##                                                                                       ##STR191##                                                 ##STR192##                                                                                       ##STR193##                                                 ##STR194##                                                                                       ##STR195##                                                 ##STR196##                                                                                       ##STR197##                                                 ##STR198##                                                                                       ##STR199##                                                 ##STR200##                                                                                       ##STR201##                                                 ##STR202##                                                                                       ##STR203##                                                 ##STR204##                                                                                       ##STR205##                                                 ##STR206##                                                                                       ##STR207##                                                 ##STR208##                                                                                       ##STR209##                                                 ##STR210##                                                                                       ##STR211##                                                 ##STR212##                                                                                       ##STR213##                                                 ##STR214##                                                                                       ##STR215##                                                 ##STR216##                                                                                       ##STR217##                                                 ##STR218##                                                                                       ##STR219##                                                 ##STR220##                                                                                       ##STR221##                                                 ##STR222##                                                                                       ##STR223##                                                 ##STR224##                                                                                       ##STR225##                                                 ##STR226##                                                                                       ##STR227##                                                 ##STR228##                                                                                       ##STR229##                                                 ##STR230##                                                                                       ##STR231##                                                 ##STR232##                                                                                       ##STR233##                                                 ##STR234##                                                                                       ##STR235##                                                 ##STR236##                                                                                       ##STR237##                                                 ##STR238##                                                                                       ##STR239##                                                 ##STR240##                                                                                       ##STR241##                                                 ##STR242##                                                                                       ##STR243##                                                 ##STR244##                                                                                       ##STR245##                                                 ##STR246##                                                                                       ##STR247##                                                 ##STR248##                                                                                       ##STR249##                                                 ##STR250##                                                                                       ##STR251##                                                 ##STR252##                                                                                       ##STR253##                                                 ##STR254##                                                                                       ##STR255##                                                 ##STR256##                                                                                       ##STR257##                                                 ##STR258##                                                                                       ##STR259##                                                 ##STR260##                                                                                       ##STR261##                                                 ##STR262##                                                                                       ##STR263##                                                 ##STR264##                                                                                       ##STR265##                                                 ##STR266##                                                                                       ##STR267##                                                 ##STR268##                                                                                       ##STR269##                                                 ##STR270##                                                                                       ##STR271##                                                 ##STR272##                                                                                       ##STR273##                                                 ##STR274##                                                                                       ##STR275##                                                 ##STR276##                                                                                       ##STR277##                                                 ##STR278##                                                                                       ##STR279##                                                 ##STR280##                                                                                       ##STR281##                                                 ##STR282##                                                                                       ##STR283##                                                 ##STR284##                                                                                       ##STR285##                                                 ##STR286##                                                                                       ##STR287##                                                 ##STR288##                                                                                       ##STR289##                                                 ##STR290##                                                                                       ##STR291##                                                 ##STR292##                                                                                       ##STR293##                                                 ##STR294##                                                                                       ##STR295##                                                 ##STR296##                                                                                       ##STR297##                                                 ##STR298##                                                                                       ##STR299##                                                 ##STR300##                                                                   ______________________________________                                    

EXAMPLE 24 Carbonated Cola Beverage

A carbonated cola beverage was prepared according to the compositiongiven below. The resulting beverage was judged to have sweetnessintensity comparable to a control beverage containing 11% sucrose.

    ______________________________________                                        Ingredient                %, weight                                           ______________________________________                                        Caffeine (1% aqueous solution)                                                                          0.700                                               L-Aspartyl-D-serine N--(cis,trans-2,6-                                                                  0.540                                               dimethylcyclohexyl)amide (10% aqueous)                                        Cola flavor concentrate   0.080                                               Phosphoric acid (50% aqueous)                                                                           0.040                                               Citric acid (50% aqueous) 0.066                                               Sodium citrate (25% aqueous)                                                                            0.210                                               Caramel color (25% aqueous)                                                                             0.370                                               Lemon oil extract         0.012                                               Lime oil extract          0.021                                               Carbonated water (3.5 volumes carbon dioxide)                                                           q.s.                                                                          100.000                                             ______________________________________                                    

Replacement of the L-aspartyl-D-serine N-(cis,trans-2,6-dimethylcyclohexyl)amide in the above formulation with 0.090%of 10% aqueous L-aspartyl-D-serine acid N-(dicyclopropylcarbinyl)amideor 1.35% of 10% aqueous L-aspartyl-D-O-methylserineN-(dicyclopropylcarbinyl)amide affords carbonated cola beverages of likequality.

EXAMPLE 25 Dietetic Hard Candy

A hard candy is prepared according to the following formulation andprocedure:

    ______________________________________                                        Ingredients                Grams                                              ______________________________________                                        L-Aspartyl-D-serine N--(dicyclopropylcarbinyl)-                                                          0.59                                               amide                                                                         Water                      4.00                                               FD and C Red #40 (10% aqueous)                                                                           0.30                                               Cherry flavor              0.60                                               Citric acid                6.00                                               Polydextrose*              420.00                                             Water                      180.00                                             ______________________________________                                         *U.S. Pat. No. 3,766,165                                                 

In a small beaker dissolve the sweetener in water, add color, flavor andcitric acid and mix well to dissolve. In a separate beaker combinepolydextrose and water. Stir while heating to 140° C. then allow to coolto 120°-125° C. Add other ingredients from small beaker and mix or kneadthoroughly. Transfer mass to an oil coated marble slab and allow to coolto 75°-80° C. Extract the mass through an oil coated impression roller.

Use of 0.49 g. of L-aspartyl-D-serineD-(2,2,4,4-tetramethyl-1,1-dioxothietan-3-yl)amide or 2.33 g. ofL-aspartyl-D-serine N-(2,2,4,4-tetramethyl-3-pentyl)amide as sweeteningagent in place of L-aspartyl-D-serine N-(dicyclopropylcarbinyl)amideaffords similar results.

EXAMPLE 26

A gelatin dessert is prepared according to the following composition andprocedure.

    ______________________________________                                        Ingredients              Grams                                                ______________________________________                                        Gelatin 225 Bloom        7.522                                                Citric acid              1.848                                                Sodium citrate           1.296                                                Strawberry flavor        0.298                                                L-Aspartyl-D-serine N--(2,2,4,4-tetramethyl-                                                           0.036                                                thietan-3-yl)amide                                                            Boiling water            240.000                                              Cold water               240.000                                                                       491.000                                              ______________________________________                                    

Premix the first five ingredients, add to boiling water and stir todissolve completely. Add cold water and stir briskly. Transfer toserving dishes and refrigerate until set.

EXAMPLE 27

Low calorie table sweeteners are prepared according to the followingformulations:

A. A powder form of sweetener is prepared by blending the followingingredients.

    ______________________________________                                        Ingredients              %, weight                                            ______________________________________                                        L-Aspartyl-D-serine N--(2,2,4,4-tetramethyl-                                                           0.42                                                 1,1-dioxothietan-3-yl)amide                                                   Crystalline sorbitol     49.52                                                Dextrin (dextrose equivalent 10)                                                                       50.00                                                Monosodium glutamate     0.02                                                 Glucono-delta-lactone    0.02                                                 Sodium citrate           0.02                                                                          100.00                                               ______________________________________                                    

One gram of the resulting blend is equivalent in sweetness to aboutthree grams of sucrose.

B. A table sweetener in liquid form is prepared as follows.

    ______________________________________                                        Ingredients               %, weight                                           ______________________________________                                        L-Aspartyl-D-serine N--(dicyclopropylcarbinyl)-                                                         0.17                                                amide                                                                         Water                     99.73                                               Sodium benzoate           0.10                                                                          100.00                                              ______________________________________                                    

One gram of the resulting solution is equivalent in sweetness to about1.2 grams of crystalline sucrose.

When the sweetener of formula (I) employed in Part A, above, is 0.83 g.of a 1:4 mixture of L-aspartyl-D-serineN-(2,2,4,4-tetramethylthietan-3-yl)amide and sodium saccharin comparableresults are obtained. Similarly when the L-aspartyl-D-serineN-(dicyclopropylcarbinyl)amide employed in Part B, above, is replaced by0.34 g. of a 1:6 by weight mixture of the same compound and sodiumsaccharin a comparable liquid table sweetener is obtained.

EXAMPLE 28 Frozen Dessert

A vanilla sugarless frozen dessert is prepared according to thefollowing formulation by conventional practice.

    ______________________________________                                        Ingredients              %, weight                                            ______________________________________                                        Heavy cream (35% butterfat)                                                                            23.00                                                Nonfat milk solids       10.50                                                Mono- and diglyceride emulsifier                                                                       0.25                                                 Polydextrose*            11.20                                                Water                    54.49                                                L-Aspartyl-D-O-methylserine N--(2,2,4,4-                                                               0.06                                                 tetramethyl-1,1-dioxothietan-3-yl)amide                                       Gelatin (225 Bloom)      0.50                                                                          100.00                                               ______________________________________                                         *U.S. Pat. No. 3,766,165                                                 

EXAMPLE 29 Canned Pears

Fresh pears are washed, peeled, cored, sliced into pieces and immersedin an aqueous solution containing 0.05% by weight of ascorbic acid. Thesliced fruit is packed into screw-cap jars and the jars filled with asyrup containing the following ingredients:

    ______________________________________                                                               %, weight                                              ______________________________________                                        Sorbitol                  25.000                                              L-Aspartyl-D-serine N--(2,2,4,4-tetramethyl-                                                            0.025                                               thietan-3-yl)amide                                                            Citric acid               0.125                                               Water                    q.s.                                                                          100.000                                              ______________________________________                                    

The jars are capped loosely and placed in an autoclave containing hotwater and processed at 100° C. for 45 minutes. The jars are removed,immediately sealed by tightening the caps and allowed to cool.

EXAMPLE 30 Powder Beverage Concentrate

    ______________________________________                                        Ingredients              %, Weight                                            ______________________________________                                        Citric acid              31.78                                                Sodium citrate           5.08                                                 Strawberry flavor        57.72                                                Strawberry FD and C color                                                                              0.54                                                 L-Aspartyl-D-O-methylserine N--(2,2,4,4-tetra-                                                         2.44                                                 methylthietan-3-yl)amide                                                      Carboxymethyl cellulose  2.44                                                                          100.00                                               ______________________________________                                    

Combine all ingredients in a blender and blend until homogeneous. Foruse, 1.73 g. of powder beverage concentrate is dissolved in 4 fluidounces (118 ml.) of water.

EXAMPLE 31 Baked Cake

A highly acceptable vanilla cake was prepared employing the followingrecipe:

    ______________________________________                                        Ingredients              Grams                                                ______________________________________                                        Emulsified shortening    16.09                                                Water                    20.83                                                Eggs                     23.00                                                Sodium bicarbonate       1.10                                                 Vanilla extract, single fold                                                                           0.28                                                 Glucono-delta-lactone    1.75                                                 Polydextrose*, 70% aqueous solution                                                                    80.00                                                Nonfat dry milk          2.50                                                 Cake flour               56.20                                                Whole milk powder        0.80                                                 Wheat starch             1.40                                                 L-Aspartyl-D-serine N--(2,2,4,4-tetramethyl-                                                           0.05                                                 thietan-3-yl)amide                                                                                     204.00                                               ______________________________________                                         *U.S. Pat. No. 3,766,165                                                 

Combine nonfat dry milk, whole milk powder, polydextrose solution andemulsified shortening. Mix at low speed until creamy and smooth (about 3minutes), add eggs and beat until a homogeneous creamy mix is obtained.Dissolve sweetener in water, add to creamy homogenate and mix 2-3minutes. Add remaining ingredients and mix until creamy and smooth (3-5minutes). Place 120 g. of batter in small pregreated pan and bake at350° F. (176° C.) for 30 minutes.

EXAMPLE 32 Synergistic Mixtures of L-Aspartyl-D-serineN-(2,2,4,4-tertramethylthietan-3-yl)amide, ##STR301##

Blends of L-aspartyl-D-serine N-(2,2,4,4-tetramethylthietan-3-yl)amideand sodium saccharin were prepared and evaluated for taste acceptabilityand sweetness intensity by comparison with aqueous sucrose standards.Sweetness potency factors of sodium saccharin and the invention compound##STR302## of 300 and 1200×sucrose, respectively, were used to calculatethe theoretical sweetness of the blends. A series of taste panelevaluations were carried out comparing aqueous solutions of theexperimental blends with sucrose solutions ranging 6 to 12% (w/v) and0.033% sodium saccharin solution. Results are tabulated below.

    __________________________________________________________________________    Blend, Parts by Weight                                                        [I, R.sup.a = CH.sub.2 OH,                                                     ##STR303##                                                                              SaccharinSodium                                                                     (T)Theory(A)ActualPotency × SucroseSweetness                                        Synergy%                                                                           QualityTaste                                __________________________________________________________________________     1         1    750   1125  50   clean,                                                                        sweet,                                                                        not                                                                           bitter                                        1         2    600   900   50   same                                          1         4    480   720   50   same                                          1         6    430   580   35   same                                          1         8    400   520   30   sweet, per-                                                                   ceptible                                                                      metallic                                                                      taste                                         1         9    390              sweet,                                                                        slight                                                                        metallic                                                                      taste                                         1         10   381              sweet,                                                                        slight to                                                                     moderate                                                                      metallic                                                                      taste                                        __________________________________________________________________________

The % synergy was calculated according to the following formula ##EQU1##where A is the actual sweetness determined by averaging the taste panelresults and T is the theoretical sweetness determined from thecomposition of the mixtures by weight e.g., for the 1:4 blend thetheoretical sweetness is (1/5×1200)+(4/5×300)=480.

From the results it is seen that with mixtures of from 1:1 to 1:8 thereis an unexpected increase in sweetness potency of 30-50%. While thereappeared to be synergy at the higher ratios, the metallic taste due tosaccharin interfered with an accurate determination. Furthermore thereis complete masking of the well known bitter aftertaste of saccharinwith blends of from 1:1 to 1:6 and effective masking of bitterness inblends containing up to one part-L-aspartyl-D-serineN-(2,2,4,4-tetramethylthietan-3-yl)amide and 8 parts sodium saccharin.

The 1:8 blend of L-aspartyl-D-serineN-(2,2,4,4-tetramethylthietan-3-yl)amide/sodium saccharin at aconcentration of 0.0192% (w/v) was found to be equivalent in sweetnessto a 10% (w/v) sucrose solution and to 1:10 saccharin/cyclamate at0.1177% (w/v).

In further sensory evaluation, a triangle test in which trained tastepanel members were presented three samples consisting of aqueoussolutions of the above 1:8 blend of invention compound/sodium saccharinat 0.0192% and 1:10 saccharin/cyclamate at 0.1177%. Panelists were askedto match the two like samples and to indicate any preference. Seven often taste panel members were not able to correctly differentiate the twosweetener blends. Of those that correctly paired the like samples, thedegree of difference between the two blends was rated as being "veryslight" or "just perceptible".

These results indicate that there is no significant difference betweenthe 1:8 blend of invention compound/saccharin and the 1:10 blend ofsaccharin/cyclamate.

When the above procedure is repeated but the invention compound employedis of the formula (I) wherein R^(a) is CH₂ OCH₂ and R is ##STR304## orwherein R^(a) is CH₂ OH and R is ##STR305## similar results areobtained.

EXAMPLE 33 Sodium Salt of L-Aspartyl-D-serineN-(dicyclopropylcarbinyl)amide

To a solution of 3.12 g. (0.01 mole) L-aspartyl-D-serineN-(dicyclopropylcarbinyl)amide in 100 ml. of ethanol is added 2 ml. of 5N sodium hydroxide. The resulting mixture is stirred for ten minutes atroom temperature then evaporated to dryness in vacuo. The residue istriturated with anhydrous ethanol, filtered and air dried.

When the sodium hydroxide employed above is replaced with an equivalentamount of potassium hydroxide, calcium hydroxide, magnesium hydroxide orammonium hydroxide the corresponding potassium, calcium, magnesium andammonium salts are formed in like manner.

The remaining L-aspartyl-amino acid dipeptide amides of formula (I) arealso converted to carboxylate salts as described above.

EXAMPLE 34 Acid Addition Salts

The L-aspartyl-D-amino acid dipeptide amide of formula (I) is slurriedin a small amount of water and an equivalent amount of an acid such ashydrochloric, phosphoric, sulfuric, acetic, maleic, fumaric, lactic,tartaric, citric, gluconic or saccharic acid is added. The resultingmixture is stirred at 15-30 minutes then evaporated to dryness orprecipitated by addition of a cosolvent such as methanol or ethanol.

PREPARATION A Alkylcycloalkylcarbinylamines anddicycloalkylcarbinylamines

i. To a mixture of 118.5 g. (1.0 mole) of cyclobutylcarbonyl chlorideand 99 g. (1.0 mole) cuprous chloride in 1000 ml. of dry ether under anitrogen atmosphere is added dropwise 478 ml. (1.0 mole) of 2 Mt-butylmagnesium chloride in the same solvent. The addition is carriedout at -5° to -15° C. The resulting mixture is poured into 500 ml. of 3M hydrochloric acid and 700 g. ice, the organic layer is separated andwashed successively with water, sodium bicarbonate solution, brine anddried (MgSO₄). The dried ether extract is evaporated at reduced pressureand the residue distilled to provide t-butylcyclobutylketone.

ii. The ketone, 105 g. (0.75 mole) is mixed with hydroxylaminehydrochloride 38.3 g. (1.16 mole) and sodium acetate, 123 g. (1.50mole), in sufficient water to effect solution, heated on the steam-bathfor one hour, cooled and the mixture adjusted to pH 7.5 with sodiumhydroxide solution. After extracting the mixture with ether, theextracts are dried (MgSO₄) and evaporated to dryness to afford theoxime. The oxime is dissolved in anhydrous ethanol (about two liters permole of oxime) and the solution heated at reflux. Sodium metal (about 10moles per mole of oxime) is added in portions at a rate sufficient tomaintain reflux temperature. When all the sodium is added the resultingmixture is cooled and 200 ml. of ethanol followed by 300 ml. of water isadded. The mixture is acidified with hydrochloric acid, evaporated toremove ethanol and the residue made alkaline (pH 12-13) with 10 M sodiumhydroxide. The alkaline mixture is extracted several times with etherand the combined extracts dried (MgSO₄). Dry hydrogen chlorine is passedthrough the dried extracts until precipitation is complete. Theprecipitated hydrochloride salt is collected by filtration, washed withether and air dried. The salt is converted to the free base by means ofaqueous sodium hydroxide, extraction with ethyl ether and evaporation ofthe extracts. The product, t-butylcyclobutylcarbinylamine is of suitablepurity for use in preparing the amides of the invention but may befurther purified, if desired, e.g. by distillation or columnchromatography.

iii. By employing the appropriate acid halide and Grignard reagent inthe above procedure in place of cyclobutylcarbonyl chloride andt-butylmagnesium chloride the following amines are obtained in likemanner.

    ______________________________________                                         ##STR306##                                                                   m        R.sup.7     R.sup.8      R.sup.9                                     ______________________________________                                        0        H           H            H                                           0        CH.sub.3    H            H                                           0        CH.sub.3    CH.sub.3     H                                           0        CH.sub.3 CH.sub.2                                                                         CH.sub.3 CH.sub.2                                                                          CH.sub.3 CH.sub.2                           0        CH.sub.3    n-C.sub.4 H.sub.7                                                                          H                                           0        (CH.sub.3).sub.2 CH                                                                       (CH.sub.3).sub.2 CH                                                                        H                                           0        CH.sub.3    CH.sub.3     C(CH.sub.3).sub.3                           1        CH.sub.3 CH.sub.2                                                                         CH.sub.3 CH.sub.2                                                                          H                                           1        n-C.sub.3 H.sub.7                                                                         H            H                                           1        CH.sub.3    CH.sub.3     H                                           1        CH.sub.3    n-C.sub.4 H.sub.7                                                                          H                                           1        n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                          H                                           1        CH.sub.3 CH.sub.2                                                                         (CH.sub.3).sub.3 C                                                                         H                                           2        CH.sub.3    CH.sub.3     CH.sub.3 *                                  2        CH.sub.3 CH.sub.2                                                                         H            H                                           2        CH.sub.3 CH.sub.2                                                                         CH.sub.3 CH.sub.2                                                                          CH.sub.3 CH.sub.2                           2        CH.sub.3    H            H                                           2        CH.sub.3    CH.sub.3     H                                           2        n-C.sub.3 H.sub.7                                                                         (CH.sub.3).sub.2 CH                                                                        H                                           2        CH.sub.3 CH.sub.2                                                                         n-C.sub.4 H.sub.7                                                                          H                                           3        CH.sub.3    CH.sub.3     CH.sub.3                                    3        n-C.sub.3 H.sub.7                                                                         H            H                                           3        CH.sub.3    CH.sub.3     H                                           4        CH.sub.3    H            H                                           4        CH.sub.3    CH.sub.3     CH.sub.3                                    4        CH.sub.3 CH.sub.2                                                                         CH.sub.3 CH.sub.2                                                                          H                                           ______________________________________                                         *B.P. 80-90° C. (21 mm.)                                          

iv. The amines of the following formula are also provided in likemanner.

    ______________________________________                                         ##STR307##                                                                            m   q                                                                ______________________________________                                                 0   1                                                                         0   2                                                                         0   3                                                                         0   4                                                                         1   1                                                                         1   2                                                                         1   3                                                                         1   4                                                                         2   2                                                                         2   3                                                                         2   4                                                                         3   3                                                                         3   4                                                                         4   4                                                                ______________________________________                                    

The following amines are also prepared by this method:

2,2-dimethyl-3-aminopentane, B.P. 123°-126° C., atmospheric pressure;

2,2,4-trimethyl-3-aminopentane, B.P. 149°-150° C., atmospheric pressure.

PREPARATION B 2,2-Dimethylcyclohexylamine

i. 2,2-Dimethylcyclohexanone

To a suspension of 13.5 g. (0.25 mole) sodium methoxide in 500 ml. ofethyl ether was added 30.8 g. (0.28 mole) 2-methylcyclohexanone and 20.3g. (0.28 mole) ethyl formate. The mixture was stirred at roomtemperature for 12 hours, filtered under a nitrogen atmosphere, thesolids washed with ethyl ether and dried in the vacuum oven at 75° C.The dried cake was ground in a mortar and pestle to a fine powder toobtain 17.5 g. (43%) of sodium 2-formyl-6-methylcyclohexanone which wasused in the next step.

The above product, 17.5 g. (0.11 mole) was added to a mixture of 2.88 g.(0.13 mole) sodium shot, 500 ml. anhydrous ammonia and about 0.1 g.ferric chloride. The resulting gray suspension was cooled to -45° C. andstirred for one hour at the reflux temperature of the system. To thiswas added 20.86 g. (0.15 mole) methyl iodide, the mixture stirred threehours at reflux and allowed to evaporate while warming to roomtemperature overnight. The residue was suspended in 300 ml. ethyl ether,refluxed to expell traces of ammonia and water added to dissolve thesolids. The ether was extracted with water (3×100 ml.), the combinedaqueous layers treated with 6 g. of solid sodium hydroxide and heated tosteam distill the ketone. The steam distillate was extracted with ethylether, the extracts washed with brine, dried and ether evaporated toprovide 2,2-dimethylcyclohexanone as a colorless liquid, 2.0 g.

ii. The ketone provided above is converted to the oxime and the latterreduced with sodium in ethanol as described in Preparation A, Part ii,to provide 3.1 g. of 2,2-dimethylcyclohexylamine.

The following 2,2-disubstituted ketones are prepared and converted toamines by the above method in like manner.

2,2-dimethylcyclopentanone

2,2-diethylcyclopentanone

2,2-di-n-propylcyclopentanone

2,2-diethylcyclohexylamine

3,3-dimethylthiepane-4-one

3,3-dimethyloxepane-4-one

4,4-dimethyloxepane-5-one

PREPARATION C 2,2,6,6-Tetramethylcyclohexylamine

i. 2,2,6,6-Tetramethylcyclohexanone

A 50% suspension of sodium hydride in mineral oil, 14.3 g. (0.30 mole),was suspended in tetrahydrofuran, the liquid decanted and the solidresuspended and decanted again to remove the oil. Then 15 g. (0.12 mole)of 2,6-dimethylcyclohexanone was added followed by dropwise addition ofa mixture of 11 g. t-butanol and 20 ml. of tetrahydrofuran (vigoroushydrogen evolution) and the resulting mixture refluxed until hydrogenevolution was complete. To this was added dropwise 37.8 g. (0.30 mole)methylsulfate and the mixture heated at reflux for 24 hours. Afterdilution with water, extraction with ethyl ether, washing the extractswith water, drying and evaporation of solvent below 40° C., 17 g. oftetramethylketone was obtained. This was distilled to obtain 14.6 g. ofproduct, B.P. 62°-64° C. (15 mm).

ii. The 2,2,6,6-tetramethylcyclohexanone (8 g.) obtained above wasconverted to the oxime and the latter compound reduced by the procedureof Preparation A, Part ii, to provide 1.4 g. of the desired amine as acolorless liquid which was of suitable purity for use as intermediate.

PREPARATION D

i. 2,2,5,5-Tetramethylcyclopentanone

To a slurry of 2.0 moles of sodium hydride (washed to remove oil) intetrahydrofuran was added 190 ml. (2.0 mole) methyl sulfate at a fastrate. Simultaneously, 35.7 g. (0.425 mole) cyclopentanone in 50 ml. ofthe same solvent was added at a slow rate. The reaction mixture warmedspontaneously to a gentle reflux and hydrogen evolution was vigorous.When the addition was completed, the mixture was allowed to stirovernight at ambient temperature. After heating to reflux for two morehours a mixture of t-butanol in tetrahydrofuran was added and refluxcontinued for three hours. The reaction mixture was diluted with water,extracted with ethyl ether, the extracts washed with water, brine, driedover anhydrous MgSO₄ and the solvent evaporated to yield 48.2 g. ofcrude product. This was distilled to afford 24.2 g. oftetramethylketone, B.P. 63°-68° C., 40 mm.

By employing a lower mole ratio of methyl sulfate to cyclopentanone, thesame method affords 2-methylcyclopentanone, 2,5-dimethylcyclopentanoneand 2,2,5-trimethylcyclopentanone.

ii. The following ketones are prepared in like manner when theappropriate starting materials are employed in the procedure of Part i,above, and Preparation C. The alpha-propyl and alpha-butylketones areprepared using e.g., the appropriate alkylbromid as alkylating agent.

2,2,6-trimethylcyclohexanone

2-ethylcyclopentanone

2,2,4,4-tetramethylcyclobutanone

2-methylcyclobutanone

2,2-dimethylcyclobutanone

2,4-diisopropylcyclobutanone

2-t-butylcyclopentanone

2,2-dimethyl-5-t-butylcyclopentanone

2,5-diisopropylcyclopentanone

2-sec-butylcyclopentanone

2-isobutylcyclohexanone

2-methylcycloheptanone

2-t-butylcycloheptanone

2,7-dimethylcycloheptanone

2,7-diisopropylcycloheptanone

3,5-dimethyltetrahydro-4H-pyran-4-one

3,5-diisopropyltetrahydro-4H-pyran-4-one

3,3,5,5-tetramethyltetrahydro-4H-pyran-4-one

3-methyl-5-t-butyltetrahydro-4H-pyran-4-one

3,3,5,5-tetramethyltetrahydro-4H-thiapyran-4-one

3-isopropyltetrahydro-4H-thiapyran-4-one

3,5-diisopropyltetrahydro-4H-thiapyran-4-one

3,-t-butyltetrahydro-4H-thiapyran-4-one

2-methyltetrahydro-4H-thiapyran-3-one

2,4-dimethyltetrahydro-4H-thiapyran-3-one

2-methylthiepane-3-one

4-methylthiepane-3-one

2,4-diethylthiepane-3-one

2,4-diisopropylthiepane-3-one

3,5-dimethylthiepane-4-one

3,3,5,5-tetramethylthiepane-4-one

4-methyltetrahydro-4H-pyran-3-one

4-sec-butyltetrahydro-4H-pyran-3-one

2-isopropyltetrahydro-4H-pyran-3-one

2,4-diisopropyltetrahydro-4H-pyran-3-one

2,4-dimethyltetrahydro-4H-pyran-3-one

2-methyloxepane-3-one

4-methyloxepane-3-one

2,4-dimethyloxepane-3-one

2,2,4,4-tetramethyloxepane-3-one

3-methyloxepane-4-one

5-methyloxepane-4-one

3,5-dimethyloxepane-4-one

3,3,5,5-tetramethyloxepane-4-one

3,5-diisopropyloxepane-4-one

3-t-butyloxepane-4-one

5-t-butyloxepane-4-one

The ketones provided above are converted to the corresponding amines byconversion to the oxime and reduction with sodium in ethanol asdescribed in Preparation A, Part ii, or Leuckart reduction of the ketoneas described in Preparation G, Part ii.

PREPARATION E 2,2,5,5-Tetramethylcyclopentylamine

A flask was charged with 35 g. (0.61 mole) of 40% sodium dispersion inmineral oil. The oil was removed by washing with ethyl ether anddecantation. The sodium was then mixed with 400 ml. of ether and amixture of 32.8 g (0.20 mole) 2,2,5,5-tetramethyladiponitrile, preparedby the method of Coffman et al., J. Am. Chem. Soc., 80, 2868 (1957), and400 ml. of tetrahydrofuran was added slowly. The resulting mixture wasstirred at room temperature for 4 hours, the excess sodium decomposed bydropwise addition of saturated aqueous ammonium chloride, the organiclayer washed with water, dried (Na₂ SO₄) and evaporated to afford 25.1g. of crude 2,2,5,5-tetramethylcyclopentylimine. The imine was dissolvedin 75 ml. of ethanol and added dropwise to a flask containing 23.3 g. (1mole) sodium shot. An additional 75 ml. ethanol was added and themixture heated at reflux until the remaining sodium metal was consumed.The reaction mixture was diluted with water, acidified to pH 1 withconcentrated hydrochloric acid, the aqueous phase washed with ether thenmade strongly basic by addition of sodium hydroxide. The organic layerwas extracted with ether, washed with brine, dried (Na₂ SO₄) andevaporated to dryness. The residue was distilled in vacuo to afford 6.6g. (23%) of the desired amine, B.P. 60°-61° C. (20 mm.).

PREPARATION F 2-Alkyl- and 2,6-Dialkylcyclohexylamines

To a solution of 25 g. of 2,6-diisopropylaniline in 250 ml. each ofethanol and water was added 10 g. of dry 5% ruthenium-on-carboncatalyst. The mixture was hydrogenated in an autoclave at 100° C., 1000psi (70.4 kg./cm.²) until hydrogen uptake ceased. The catalyst wasremoved by filtration and the filtrate evaporated to remove solvent. Theresidue was distilled in vacuo to obtain 11.2 g. of2,6-diisopropylcyclohexylamine as a mixture of cis,trans andtrans,trans-isomers, B.P. 122°-124° C. at 22 mm.

By employing the appropriate 2-alkylaniline or 2,6-dialkylaniline asstarting material and hydrogenating by the above method the followingcyclohexylamines are also obtained.

2-methyl-6-ethylcyclohexylamine, B.P. 82°-87° C. at 19 mm. (50% yield);

2-methyl-6-isopropylcyclohexylamine, B.P. 86° at 14 mm. (45% yield);

2-n-butylcyclohexylamine;

2-ethyl-6-n-butylcyclohexylamine;

2-methyl-6-t-butylcyclohexylamine;

2-t-butylcyclohexylamine;

2,6-dimethylcyclohexylamine;

trans-2-ethylcyclohexylamine, B.P. 77°-78° (23 mm.);

2,6-diethylcyclohexylamine, B.P. 96° C., (17 mm.);

trans-2,-isopropylcyclohexylamine;

2-isobutylcyclohexylamine;

2-methyl-6-n-butylcyclohexylamine.

PREPARATION G 2-t-Butylcyclohexylamine

i. 2-t-Butylcyclohexanone

A solution of 31.25 g. (0.20 mole) t-butylcyclohexanol in 80 ml. ofethyl ether was cooled to 10° C. To this was added dropwise, withstirring, a solution of 21.0 g. (0.07 mole) sodium dichromate dihydrateand 15.75 ml. (0.30 mole) concentrated sulfuric acid in 100 ml. waterwhile maintaining the reaction mixture below 25° C. The mixture was thenwarmed to room temperature, stirred for two hours, poured ontoice-water, ether layer separated, the aqueous phase extracted again withether and the combined extracts washed with water, sodium bicarbonateand dried (MgSO₄). Evaporation of the ether afforded 30.6 g. (99%) ofthe desired ketone.

ii. Leuckart Reduction of Ketone

A mixture of 2-t-butylcyclohexanone 30.6 g. (0.20 mole), formamide 50ml. (1.2 mole) and formic acid (10 ml.) was heated at reflux whileremoving water as it formed in the reaction while returning the ketoneto the reaction vessel. Formic acid (10 ml.) was added as needed tocontrol deposition of ammonium carbonate in the condenser. After fourhours the reaction temperature reached 197° C. and distillation ceased.The mixture was cooled, diluted with water (50 ml.) and extracted withethyl acetate (75 ml.). The organic layer was evaporated, concentratedhydrochloric acid added (50 ml. per 100 ml. of residue), the mixtureboiled overnight, cooled and washed with 50 ml. of ethyl ether. Theaqueous phase was adjusted to pH 11 with sodium hydroxide, cooled,extracted with ether (2×40 ml.) and the extracts dried over sodiumhydroxide pellets. The solvent was evaporated and the residue distilledthrough a 10 cm. column to obtain 21.93 g. of the title amine (71%),B.P. 86°-88° C. (21 mm.) as a mixture of cis and trans-isomers.

iii. dl-Fenchone and l-fenchone are reduced to the correspondingfenchylamines by the Leuckart reduction method of Part ii, above.(-)Fencylamine is obtained as a water white liquid, B.P. 55°-60° C. (6mm.), [alpha]_(D) -21.9° in 30% yield.

PREPARATION H 2,4-Dimethyl-3-aminopentane

In a shaker bottle was placed 0.2 g. platinum dioxide and 10 ml. water.The slurry was hydrogenated at 50 psi (3.5 kg./cm².) for 15 minutes. Tothe resulting slurry of platinum black was added 34.26 g. (0.30 mole)2,4-dimethyl-3-pentanone, 20.0 g. (0.37 mole) ammonium chloride, 225 ml.ammonia saturated methanol and 25 ml. concentrated ammonium hydroxide.The resulting slurry was hydrogenated at 60 psi (4.2 kg./cm.²) and roomtemperature for 20 hours, filtered, refluxed for for 1 hour and cooled.The mixture was adjusted to pH 2.0 with concentrated hydrochloric acidand the volume was reduced by evaporation at reduced pressure. Afterwashing with 75 ml. ethyl ether, the aqueous solution was brought to pH13 with 10 M sodium hydroxide solution and extracted with three 100 ml.portions of ether. The extracts were combined, dried over anhydrousMgSO₄ and saturated with gaseous hydrogen chloride. The precipitatedamine hydrochloride was collected by filtration, air dried anddecomposed with 75 ml. 10 M sodium hydroxide solution. The oily aminelayer was separated and distilled at atmospheric pressure, B.P.129°-132° C., yielding 17.6 g.

PREPARATION I trans-2-Ethylcyclopentylamine

i. 2-Ethylcyclopentanone

In a three-necked flask 5.0 g. of sodium metal was dissolved in 250 ml.of dry ethanol and 31.24 g. (0.20 mole) 2-carboethoxycyclopentanoneadded. To the resulting yellow solution 18.4 ml. (0.23 mole) ethyliodide was added dropwise and the mixture heated at reflux for twohours. After cooling, 250 ml. of brine and 50 ml. of water were addedand the mixture extracted with ethyl ether (2×100 ml.). After drying(MgSO₄) and evaporation of solvent 36.5 g. (99%) of2-ethyl-2-carboethoxycyclopentanone was obtained.

This was decarboxylated by heating at reflux with a mixture of 200 ml.of concentrated hydrochloric acid and 100 ml. of water. After four hoursat reflux carbon dioxide evolution was complete. The mixture was cooled,saturated with sodium chloride, extracted with ethyl ether, the extractsdried (MgSO₄) and ether evaporated. The residue was distilled to obtain12.62 g. (56%) of 2-ethylcyclopentanone, B.P. 97°-98° C. (100 mm).

ii. The product obtained above was converted totrans-2-ethylcyclopentylamine by the procedure of Preparation A, Partii, B.P. 150°-151° C. in 35% yield. The identity of the product wasverified by its ¹ H-NMR spectrum.

By employing the appropriate 2-carbethoxycycloalkanone or acorresponding hetercyclic ketone (prepared by the well known Dieckmanncyclization of the appropriate dicarboxylate ester, see e.g., H. O.House, "Modern Synthetic Reactions", W. A. Benjamin, Menlo Park, Calif.,1972, p. 740.) and the appropriate alkyl halide in place of ethyl iodidein the above procedure the following amines of formula RNH₂ are preparedin like manner.

Where R is

    ______________________________________                                         ##STR308##                                                                   m                   R.sup.3                                                   ______________________________________                                        1                   CH.sub.3                                                  1                   C.sub.2 H.sub.5                                           2                   t-C.sub.4 H.sub.9                                         2                   CH.sub.3                                                  2                   sec-C.sub.4 H.sub.9                                       4                   CH.sub.3                                                  4                   t-C.sub.4 H.sub.9                                         ______________________________________                                    

Where R is

    ______________________________________                                         ##STR309##                                                                   X           n     p             R.sub.3                                       ______________________________________                                        O           1     0             2-CH.sub.3                                    O           1     0             4-CH.sub.3                                    O           1     0             2-t-C.sub.4 H.sub.9                           O           0     2             2-CH.sub.3                                    O           0     2             4-CH.sub.3                                    O           0     2             4-sec-C.sub.4 H.sub.9                         O           0     2             2-i-C.sub.3 H.sub.7                           O           0     3             2-CH.sub.3                                    O           0     3             4-CH.sub.3                                    O           1     2             3-CH.sub.3                                    O           1     2             5-CH.sub.3                                    O           1     2             5-t-C.sub.4 H.sub.9                           O           1     2             3-t-C.sub.4 H.sub.9                           S           0     1             2-CH.sub.3                                    S           0     1             4-CH.sub.3                                    S           1     1             i-C.sub.3 H.sub.7                             SO.sub.2    1     1             t-C.sub.4 H.sub.9                             S           0     2             2-CH.sub.3                                    S           0     3             2-CH.sub.3                                    S           0     3             4-CH.sub.3                                    ______________________________________                                    

PREPARATION J trans-2-Isopropylcyclopentylamine

i. 2-Isopropylcyclopentanone

To a solution of 10 g. of sodium metal in 670 ml. of ethanol was addeddropwise a mixture of 100 g. (1.19 mole) cyclopentanone and 60 g. (1.03mole) acetone and the resulting mixture refluxed for 1.5 hours. Thesolvent was evaporated in vacuo, the residue taken up in ether, thesolution washed with 3 M hydrochloric acid (5×200 ml.), 5% sodiumbicarbonate (3×200 ml.), brine (1×200 ml.) and dried (MgSO₄). The etherwas evaporated with mild heating to afford 97 g. of dark liquid whichwas distilled in vacuo to obtain 55 g. of2-isopropylidenecyclopentanone, B.P. 96°-100° (2.7 mm.).

To 12.75 g. of the above product in 250 ml. of methanol was added 2.0 g.5% palladium-on-carbon catalyst and the mixture hydrogenated at 50 psi(3.5 kg./cm².). After one hour the hydrogen uptake was complete. Thecatalyst was removed and solvent evaporated in vacuo to afford 12.75 g.of colorless liquid. This was distilled to obtain 9.64 g. of2-isopropylcyclopentanone, B.P. 74°-76° C. (20 mm.).

Reduction of 2-isopropylcyclopentanone by the method of Preparation A,Part ii afforded the corresponding amine, B.P. 167° (atm.) in 31% yield.

PREPARATION K 2,2-Dimethyl-3-aminobutane

In a 500 ml. flask was placed 10.0 g. (0.10 mole)2,2-dimethyl-3-butanone, 250 ml. methanol, 76.94 g. (1.0 mole) ammoniumacetate and 4.37 g. (0.07 mole) sodium cyanoborohydride, and the mixturewas allowed to stir at room temperature for 24 hours. The pH wasadjusted to 2.0 with concentrated hydrochloric acid and the methanolremoved at reduced pressure. The residual solid was dissolved in 500 ml.water and washed with three 100 ml. portions of ether. The pH of theaqueous solution was adjusted to 13 with 10 M sodium hydroxide and themixture extracted with three 100 ml. portions of ether. The extractswere combined, dried over anhydrous MgSO₄, filtered and distilled. Theamine (2.4 g.) distilled at 102°-103° C. at atmospheric pressure.

The racemic amine was resolved by the Polarimetric Control methoddescribed by Bruck et al., J. Chem. Soc., 921 (1956) employing the aminehydrogen tartarates and crystallizing from 70:30 methanol/water (byvolume) to obtain dextrorotatory amine of 93±4% purity and levorotatoryamine of 80±4% purity.

When an equivalent amount of 2,2-dimethyl-3-pentanone is employed inplace of 2,2-dimethyl-3-butanone in the above procedure2,2-dimethyl-3-aminopentane is obtained and resolved into itsenantiomers.

PREPARATION L L-Aspartic acid N-thiocarboxyanhydride

A. L-Aspartic acid (582 g., 4.29 mole) was added gradually with stirringto 350.9 g. (8.58 mole) of 50% sodium hydroxide solution at 0° C. Methylmethyl xanthate (550 g., 4.51 mole) in 405 ml. of methanol was thenadded as rapidly as possible. The mixture was heated at 45° C. for 1.5hours, cooled to room temperature, and washed with two portions ofmethylene chloride. The methylene chloride washes were discarded and theaqueous phase acidified with concentrated hydrochloric acid at 0° C. Thesolution was extracted with three portions of ethyl acetate, and thecombined extracts washed with brine and dried over anhydrous magnesiumsulfate. The solvent was evaporated in vacuo to give a yellow oil whichcrystallized upon addition of ethylene dichloride and n-hexane. TheN-methoxy-thiocarbonyl-L-aspartic acid was collected by filtration,washed with fresh n-hexane, and dried (420 g., 47%).

M.P. 128°-130° C., ¹ H-NMR (DMSO-d₆), (delta) 2.73 (d, 2H, J=6 Hz), 3.63(s, 3H), 4.43 (dt, 1H, J=6 Hz, 8 Hz), 6.63 (d, 1H, J=8 Hz); infraredspectrum (KBr) 1715, 1515 cm⁻¹.

B. N-methoxythiocarbonyl-L-aspartic acid (207.0 g., 1.00 mole) wasdissolved in 1200 ml. ethyl acetate at 0° C. and phosphorous tribromide(47 ml., 0.50 mole) was added in one portion. The cooling bath wasremoved and the temperature allowed to rise spontaneously to 35° C. Thesolution was stirred for 10 minutes after which time a granular whiteprecipitate had formed. The reaction mixture was cooled to 0°-5° C., theproduct collected by filtration, washed with a small volume of ether,and dried. The yield of analytically pure L-aspartic acidN-thiocarboxyanhydride was 157.4 g. (90%).

M.P. 200°-205° C. (dec.); [alpha]_(D) ²⁵ =-109.5° (C=1, THF); infraredspectrum (KBr) 3225, 1739, 1724, 1653, 1399 cm⁻¹ ; ¹ H-NMR (DMSO-d₆) ppm(delta) 2.83 (d, 2H, J=5.0 Hz), 4.70 (t, 1H, J=5.0 Hz), 9.23 (bs, 2H,ex); mass spectrum (m/e) 175 (M⁺), 87, 60.

PREPARATION M 2,2,3,3-Tetramethylcyclopropylamine

i. Ethyl 2,2,3,3-Tetramethylcyclopropanecarboxylate

The method of Mesheheryakov, Chem. Abstr., 54, 24436d (1960) wasemployed. To a mixture of 19 g. (0.226 mole) of 2,3-dimethyl-2-buteneand 2 g. of cupric sulfate is added at reflux a mixture of 51 g. (0.447mole) ethyl diazoacetate and 19 g. of 2,3-dimethyl-2-butene. Theresulting mixture is heated at reflux for 3 hours, cooled, filtered anddistilled to afford 19.8 g. (26%) of the desired cyclic ester, B.P.76°-77° (15 mm.).

ii. To 300 ml. of ethanol containing 40 g. of ammonia is added 17 g.(0.10 mole) of the ester obtained above and the resulting mixtureallowed to stand overnight. After heating at reflux for one hour theethanol was evaporated in vacuo to obtain2,2,3,3-tetramethylcyclopropanecarboxamide.

A solution of 2.82 g. (0.02 mole) of the amide in 8 ml. tetrahydrofuranand 4 ml. of water is cooled to 5° C. and 10 ml. of 2 M sodiumhypochlorite added dropwise followed by 8 ml. of 20% (w/v) sodiumhydroxide. The two phase mixture is stirred at 5° C. for 30 minutes thenat 20° C. for one hour. The organic layer is extracted with ether, theether layer extracted with 2 M hydrochloric acid (3×20 ml.), the aqueousacidic layer is made strongly alkaline with sodium hydroxide andextracted with ether. The extracts are dried (Na₂ SO₄) and the etherevaporated at 25° (50 mm.) to give 0.67 g. (25%)2,2,3,3-tetramethylcyclopropylamine. ¹ H-NMR (CDCl₃) ppm (delta):

0.95 (6H, singlet); 1.00 (6H, singlet); 1.83 (1H, multiplet); 1.7 (2H,multiplet).

iii. The following substituted cyclopropylamines are prepared in ananalogous fashion from the appropriate olefin.

    ______________________________________                                         ##STR310##                                                                   R.sup.3       R.sup.4   R.sup.5 R.sup.6                                       ______________________________________                                        CH.sub.3      H         CH.sub.3                                                                              H                                             CH.sub.3      H         H       H                                             i-CH.sub.3 H.sub.7                                                                          H         H       H                                             i-C.sub.3 H.sub.7                                                                           H         i-C.sub.3 H.sub.7                                                                     H                                             CH.sub.3      CH.sub.3  H       H                                             t-C.sub.4 H.sub.9                                                                           H         H       H                                             CH.sub.3      CH.sub.3  t-C.sub.4 H.sub.9                                                                     H                                             ______________________________________                                    

PREPARATION N 3-Amino-2,2,4,4-tetramethyloxetane

To 13.6 g. (0.12 mole) of diisopropylketone is added 0.2 ml. ofphosphorus tribromide. To this is added dropwise at 10° C., 38.4 g.(0.24 mole) bromine and the mixture warmed to 55°-60° C. and held atthis temperature for 1.5 hours. After cooling and partioning betweenchloroform and water, the organic layer is washed with sodium carbonatesolution until neutral, dried and the solvent evaporated to obtain2,4-dibromo-2,4-dimethylpentan-3-one.

To 0.1 mole of the dibromoketone in 160 ml. of ethanol is added asolution of 8 g. of sodium hydroxide in 80 ml. water and the resultingmixture is stirred at room temperature for 30 minutes. After dilutingwith water the reaction mixture is extracted with ethyl ether, theextracts washed with water, brine and dried (MgSO₄). The ether isevaporated to provide 2,4-dihydroxy-2,4-dimethyl-3-pentanone. This isdissolved in 50 ml. chloroform and 1.5 ml. concentrated sulfuric acidadded dropwise. The resulting mixture is heated at reflux for five hourswhile removing water as its azeotropic mixture with chloroform. When nomore water is evolved the reaction mixture is washed with water, theorganic layer dried (MgSO₄) and solvent evaporated to provide2,2,4,4-tetramethyloxetane-3-one which is purified by distillation.

The ketone is converted to the oxime and reduced with sodium/ethanol bythe procedure of Preparation A, Part ii.

PREPARATION O 3-Amino-2,2-dimethyloxetane

3-Hydroxy-3-methyl-2-butanone, 0.20 mole, is treated dropwise with aequimolar amount of bromine at room temperature and the resultingmixture stirred for three hours. The mixture is taken up in chloroform,washed with sodium carbonate solution until neutral, dried and solventevaporated to obtain 1-bromo-3-hydroxy-3-methyl-2-butanone.

To 0.1 mole of the bromoketone in 160 ml. of ethanol is added a solutionof 4 g. of sodium hydroxide in 80 ml. water and the mixture stirred atroom temperature for 30 minutes. The mixture is diluted with water,extracted with ether, the extracts washed with water, brine and dried(MgSO₄). The solvent is evaporated and the residue taken up in 50 ml. ofchloroform. To this is added dropwise 1.5 ml. of concentrated sulfuricacid and the resulting mixture heated at reflux while removing water asits azeotrope with chloroform. When water evolution is complete theresulting ketone is isolated and converted to the desired amine asdescribed in Preparation N.

PREPARATION P

Employing the procedures of Preparation N and O but starting with theappropriate ketone or alpha-hydroxyketone in each case the followingamines are prepared in like manner.

    ______________________________________                                         ##STR311##                                                                   R.sup.3      R.sup.4   R.sup.5     R.sup.6                                    ______________________________________                                        CH.sub.3     H         H           H                                          CH.sub.3     H         t-C.sub.4 H.sub.9                                                                         H                                          CH.sub.3     C.sub.2 H.sub.5                                                                         CH.sub.3    C.sub.2 H.sub.5                            CH.sub.3     H         CH.sub.3    H                                          CH.sub.3     CH.sub.3  C.sub.2 H.sub.5                                                                           C.sub.2 H.sub.5                            i-C.sub.3 H.sub.7                                                                          H         H           H                                          i-C.sub.3 H.sub.7                                                                          H         i-C.sub.3 H.sub.7                                                                         H                                          C.sub.2 H.sub.5                                                                            C.sub.2 H.sub.5                                                                         H           H                                          ______________________________________                                    

PREPARATION Q Dicyclopropylcarbinylamine

In a 500 ml. round bottom flask was placed 41.7 g. (0.60 mole)hydroxylamine hydrochloride and 80 ml. water. With stirring, 44 ml. of10 M sodium hydroxide solution and 44.4 g. (0.40 mole) dicyclopropylketone were added. The mixture was stirred at reflux for three hours.After cooling, 60 ml. methylene chloride was added and the mixturestirred until all oxime had dissolved. The methylene chloride layer wasseparated and dried over anhydrous magnesium sulfate. The solvent wasremoved by evaporation at reduced pressure and the residuerecrystallized from 55 ml. hexane, yielding 40.0 g.dicyclopropylketoxime, M.P. 69°-72° C.

In a 500 ml., three-necked round bottom flask was placed 18.8 g. (0.15mole) dicyclopropylketoxime and 150 ml. anhydrous ethanol. Withefficient stirring 19.2 g. (0.83 mole) sodium spheres was added inportions as rapidly as possible, maintaining reflux throughout theaddition. Following dissolution of the sodium, the reaction was cooledto 60° C. and 60 ml. water was added. After cooling, 78 ml. concentratedhydrochloric acid was added dropwise with stirring. Ethanol wasdistilled at reduced pressure and 50 ml. water added to dissolve salts.The mixture was adjusted to pH 13 with 10 M sodium hydroxide solutionand extracted with three 40 ml. portions of methylene chloride. Theextracts were combined, dried over anhydrous magnesium sulfate, filteredand evaporated at reduced pressure. The residual amine was distilled at88°-90° C./95 mm Hg, yielding 11.0 g. of the desired product.

PREPARATION R 2-Amino-3,3-dimethyl-gamma-butyrolactone Hydrochloride

The method is that of Nagase et al., Chem. Pharm. Bull., 17, 398 (1969).

To a stirred solution of 2,2-dimethylhydroacrylaldehyde [prepared fromsec-butyraldehyde and formaldehyde by the method of Stiller, et al., J.Am. Chem. Soc., 62, 1785 (1940)] 5.11 g. in methanol (25 ml.), asolution of ammonium chloride, 2.94 g., and sodium cyanide, 2.9 g., inwater (40 ml.) is added dropwise. After stirring for three hours themixture is saturated with ammonia gas and allowed to stand at roomtemperature overnight. The resulting mixture is concentrated in vacuo toa small volume and 40 ml. of concentrated hydrochloric acid is added.After refluxing for three hours the mixture is evaporated in vacuo andthe residue crystallized from ethanol-ethyl ether and then from ethanolto give 2.2 g. of the title compound, M.P. 214°-215° C. (dec.).

Use of homologs of 2,2-dimethylhydracrylaldehyde in the above procedureaffords the corresponding compounds of the formula ##STR312## where oneof R¹² and R¹³ is alkyl having from one to four carbon atoms and theother is hydrogen or alkyl having from one to four carbon atoms.

PREPARATION S 4-Amino-3,3,5,5-tetramethyl-tetrahydro-4H-pyran-2-one

i. Methyl 5-Hydroxy-2,2,4,4-tetramethyl-3-ketovalerate

A mixture of 172 g. (1.0 mole) methyl 2,2,4-trimethyl-3-ketovalerate,5.4 g. (0.10 mole) sodium methoxide and 33 g. (0.36 mole) paraformaldein 250 ml. methanol is heated at reflux for eight hours. The mixture isquenched by addition of water, neutralized with hydrochloric acid,extracted with ethyl ether, washed with water, brine and solventevaporated. The residue is purified by vacuum distillation orchromatography on silica gel to provide the purified product.

ii. 2,2,4,4-tetramethyl-2,4-dioxotetrahydro-4H-pyran

A solution of 101 g. (0.50 mole) of the above product in 200 ml.methanol and 20 ml. concentrated hydrochloric acid is heated at refluxfor two hours, cooled, poured into ice-water, extracted with ethylether, the extracts washed with sodium bicarbonate solution, water,dried and evaporated to dryness. The residue was heated in vacuo at80°-100° C. for two hours to obtain product of suitable purity for usein the next step.

iii. The ketolactone obtained above is converted to the corresponding4-oximino derivative and this reduced to the title compound by theprocedure of Preparation Q.

PREPARATION T 4-Amino-3,3,5,5-tetramethyl-2-piperidone

i. Methyl 5-Dibenzylamino-2,2,4,4-tetramethyl-3-ketovaleratehydrochloride

To a mixture of 86 g. (0.50 mole) methyl 2,2,4-trimethyl-3-ketovalerate,117 g. (0.64 mole) dibenzylamine hydrochloride and 19.8 g. (0.22 mole)paraformaldehyde is added a solution of 1 ml. of concentratedhydrochloric acid in 150 ml. 95% ethanol and the mixture is heated atreflux for four hours. The mixture is filtered, 500 ml. of hot acetoneadded to the filtrate and the resulting mixture cooled then refrigeratedovernight. The precipitated product is collected by filtration, washedwith acetone and dried.

ii. 3,3,5,5-tetramethylpiperidin-2,4-dione

The above hydrochloride salt is partitioned between 0.1 N sodiumhydroxide solution and ethyl ether. The ether extracts are dried (MgSO₄)evaporated to dryness and the residue taken up in methanol. To themethanol solution is added 1 g. of 10% Pd/C and the mixture hydrogenatedat 3-4 atmospheres pressure until hydrogen uptake is complete. Thecatalyst is removed by filtration, the filtrate heated at reflux for twohours, solvent evaporated and the residue heated at 70°-80° C. in vacuofor two hours. The residual product is purified by chromatography onsilica gel.

iii. The piperidinedione obtained above is converted to the 4-oximinoderivative and this reduced to the title 4-amino analog by the procedureof Preparation Q.

PREPARATION U 3,3,5,5-Tetramethylpyrrolidin-2,4-dione

A mixture of 80 g. of 2,2,4,4-tetramethyl-1,3-cyclobutanedione monoxime,prepared by the method of U.S. Pat. No. 3,125,569, and 250 ml. 98% (w/w)sulfuric acid was warmed at 50°-60° C. for one hour and allowed to standovernight at room temperature. The reaction mixture was poured onto 800g. ice, extracted with methylene chloride, the extracts washed withsodium bicarbonate solution, water, dried (MgSO₄) and evaporated toremove solvent. The resulting mixture of products was purified by columnchromatography on silica gel and the fractions containing the titlecompound combined and evaporated to dryness.

The ketolactam thus obtained is converted to3-amino-3,3,5,5-tetramethyl-2-pyrrolidone by methods described above.

PREPARATION V 3-Amino-2,2,4,4-tetramethylthietan and its 1,1-Dioxide

A. 2,4-Dibromo-2,4-dimethylpentan-3-one

To 136 g. (1.2 mole) of diisopropylketone was added 2 ml. of phosphorustribromide and the mixture cooled to 10° C. To this was added dropwise384 g. (2.4 mole) of bromine, the mixture allowed to warm to roomtemperature. After two hours at this temperature the mixture was warmedat 55°-60° C. for one hour then cooled and partioned between chloroformand water. The water was discarded and the organic layer washed withsodium carbonate solution until neutral. The organic layer was dried(MgSO₄) and solvent evaporated to obtain 316 g. (97%) of the desiredproduct.

B. 2,2,4,4-Tetramethyl-3-oxothietane

Sodium metal, 23 g. (1.0 mole), was dissolved in 500 ml. of dry methanoland the resulting mixture cooled to 10° C. Hydrogen sulfide gas waspassed through the mixture until it was saturated. Then 136 g. (0.5mole) of the dibromoketone obtained in Part A was added dropwise whilecontinuing to allow hydrogen sulfide to pass through the reactionmixture. After the addition was completed the mixture was stirred fortwo hours at 10° C., allowed to warm to room temperature and stirredovernight. After pouring the reaction mixture into water, it wasextracted with ethyl ether and the extracts washed with dilutehydrochloric acid and brine. After drying over magnesium sulfate theether was evaporated, the residue slurried with methanol, cooled andfiltered to obtain 46 g. (64%) of solid product which was used withoutpurification in the next step.

C. Reductive amination of ketone

To 75 ml. of dry methanol was added 4.5 g. (0.031 mole) of2,2,4,4-tetramethyl-3-oxothietane, 23.9 g. (0.31 mole) ammonium acetateand 1.36 g. (0.0217 mole) sodium cyanoborohydride and the resultingmixture heated at reflux for four hours. Additional sodiumcyanoborohydride (1.36 g.) was added and refluxing continued for threedays with a third increment of the same reagent added at the start ofthe third day. The resulting mixture was acidified to pH 2 withhydrochloric acid and evaporated to dryness on the rotary evaporator atreduced pressure. The residue was dissolved in water, washed with ethylether, the aqueous phase adjusted to pH 11 with sodium hydroxidesolution and extracted with ethyl ether. The extracts were washed withbrine, dried (MgSO₄) and evaporated to dryness to obtain 1.9 g. (42%) ofthe desired amine as a crystalline solid. The structure of the productwas verified by its ¹ H-NMR spectrum.

D. 3-Amino-2,2,4,4-tetramethylthietane-1,1-dioxide

The amine obtained in Part C, above, 29 g. (0.2 mole) was dissolved in50 ml. acetonitrile and 250 ml. water added. While maintaining themixture at pH 10 with sodium hydroxide, 35.8 g. (0.21 mole) carbobenzoxychloride was added over 30 minutes, the mixture stirred for one hour,filtered, the precipitate washed with water and dried in vacuo at 50° C.to provide the NCbz-amine, R_(f) 0.7 (hexane/ethyl acetate 4:1 v/v,phosphomolybdic acid spray), 52.1 g. (93.4%). This was dissolved in 700ml. methylene chloride, 77 g. (0.372 mole) m-chloroperbenzoic acid wasadded slowly while maintaining the temperature below 45° C. (20°-42°C.). The precipitated solid was collected by filtration, the filtratewas washed with 1 N hydrochloric acid, aqueous sodium bicarbonatesolution, dried (MgSO₄) and the solvent evaporated. The residue wascrystallized from acetone-water to obtain 42 g. (73%) of theCbz-protected amine 1,1-dioxide, R.sub. f 0.7 (hexane/ethyl acetate 1:1v/v, phosphomolybdic acid spray).

The protecting group was removed by hydrogenolysis of 5 g. of Cbz-aminein 250 ml. methanol, 5 ml. concentrated hydrochloric acid and 2 g. of 5%Pd/C (50% wet). The product was isolated in the usual manner. Yield: 2.4g. (85%), R_(f) 0.6. The retention time upon gas-liquid chromatographyon a 1 meter, OV-1 column at 180° C. was 1.3 minutes. The overall yieldfor the three steps starting from 3-amino-2,2,4,4-tetramethylthietanewas 65%.

By employing equivalent amounts of amine and m-chloroperbenzoic acid inthe above procedure the corresponding sulfoxide is obtained in likemanner.

E. Employing the appropriate ketone of formula R³ R⁴ CHCOCHR⁵ R⁶ inplace of diisopropylketone in the procedures of Parts A-C affords thecorresponding amines of the formula shown below.

    ______________________________________                                         ##STR313##                                                                   R.sup.3   R.sup.4      R.sup.5 R.sup.6                                        ______________________________________                                        CH.sub.3  H            CH.sub.3                                                                              H                                              CH.sub.3  H            H       H                                              C.sub.2 H.sub.5                                                                         H            H       H                                              i-C.sub.3 H.sub.7                                                                       H            H       H                                              i-C.sub.3 H.sub.7                                                                       H            i-C.sub.3 H.sub.7                                                                     H                                              t-C.sub.4 H.sub.9                                                                       H            H       H                                              t-C.sub.4 H.sub.9                                                                       H            t-C.sub.4 H.sub.9                                                                     H                                              n-C.sub.4 H.sub.9                                                                       H            n-C.sub.4 H.sub.9                                                                     H                                              C.sub.2 H.sub.5                                                                         H            C.sub.2 H.sub.5                                                                       H                                              ______________________________________                                    

The corresponding sulfoxides and sulfones are prepared by the procedureof Part D above.

PREPARATION W 3-Amino-2,2,4,4-tetramethyltetrahydrothiophene

A. 1-Hydroxy-2,2,4-trimethylpentan-3-one

To sodium methoxide prepared from 7.5 g. of sodium metal and 250 ml. ofmethanol was added 72.5 g. (2.4 moles) paraformaldehyde followed by 250g. (2.2 moles) diisopropylketone and the resulting mixture heated atreflux for three hours. The reaction was quenched with water,neutralized with hydrochloric acid, extracted with ethyl ether, washedwith water, brine and the solvent evaporated. The residual oil (90 g.)was distilled in vacuo to obtain 28 g. of the desired product boiling at92°-98° C. at 16-20 mm. GLC on OV-1 column at 107° C., retention time314 sec., 96% pure.

When the above procedure was repeated on the same scale but the reactionmixture refluxed for 16 hours, 31 g. of product was obtained of 96%purity by GLC.

B. 4-Bromo-1-hydroxy-2,2,4-trimethylpentan-3-one

To a stirred, refluxing solution of 69 g. (0.48 mole) of1-hydroxy-2,2,4-trimethylpentan-3-one in 500 ml. of chloroform was addeddropwise a solution of 77 g. (0.48 mole) bromine in 100 ml. ofchloroform. When the addition was completed the mixture was stirred atreflux for one hour, allowed to cool and stand overnight at roomtemperature. Evaporation of solvent at reduced pressure afforded 127 g.of product which was used in the next step without purification.

C. 2,2,4,4,-Tetramethyltetrahydrothiophen-3-one

The product obtained in Part B, 79 g. (0.3 mole) was dissolved in 300ml. of dry pyridine, cooled to 0° C. and 114 g. (0.6 mole) ofp-toluenesulfonyl chloride was added in portions at 0° C. The resultingmixture was stirred at this temperature for 3 hours, 15 minutes, pouredinto ice/water and extracted with ethyl ether. The extracts were washedwith dilute hydrochloric acid, water and brine then dried over anhydrousmagnesium sulfate. The solvent was evaporated to provide 111 g. (98%) ofcrystalline tosylate.

The tosylate, 94 g. (0.25 mole) was dissolved in one liter of pyridine,180 g. (0.75 mole) of sodium sulfide monohydrate added and the mixtureheated to 75° C. and held at this temperature for one hour and allowedto stand at room temperature overnight. Water was added and the mixturewas extracted with ether. The extracts washed with hydrochloric acid,brine, dried (MgSO₄) and the solvent evaporated to obtain 35 g. of thetitle compound, 89% yield. The product showed only one spot upon silicagel TLC, eluting with ethyl acetate/hexane (1:4 by volume, R_(f) 0.5.The ¹ H-NMR spectrum was in agreement with the structure for the titlecompound.

D. Leuckart reduction of ketone

To a 100 ml. round-bottomed three-necked flask fitted with stirrer,thermometer and condenser with fractionating head was added 10.0 g.(0.063 mole) of 2,2,4,4-tetramethyltetrahydrothiophen-3-one, 15.2 ml.(0.38 mole) formamide and 3.5 ml. (0.092 mole) formic acid and themixture heated at reflux (163° C.) while removing water. The reactionmixture was maintained at 160°-180° C. for 20 hours with addition offormic acid (10 ml.) at intervals. The pot temperature increased to 200°C. over this period. The reaction mixture was cooled, water added andthe mixture extracted with ethyl acetate. The extracts were evaporatedin vacuo. The residue was refluxed with 20 ml. of 6 N hydrochloric acidfor two hours, cooled, the resulting mixture washed with ethyl ether,the aqueous phase adjusted to pH 11 with sodium hydroxide solution andextracted with ethyl ether. The extracts were dried and evaporated toobtain 2 g. of 3-amino-2,2,4,4-tetramethyltetrahydrothiophene which wasidentified by ¹ H-NMR and appeared homogeneous upon silica gel TLC.

E. By employing the appropriate ketone as starting material in place ofdiisopropylketone in the above procedures and that of Preparation X, thefollowing amines are similarly obtained.

    ______________________________________                                         ##STR314##                                                                   X      R.sup.3    R.sup.4   R.sup.5  R.sup.6                                  ______________________________________                                        S      CH.sub.3   H         CH.sub.3 H                                        S      H          H         CH.sub.3 H                                        S      CH.sub.3 CH.sub.2                                                                        H         CH.sub.3 CH.sub.2                                                                      H                                        S      (CH.sub.3).sub.2 CH                                                                      H         (CH.sub.3).sub.2 CH                                                                    H                                        S      CH.sub.3   CH.sub.3  H        H                                        O      CH.sub.3 CH.sub.2                                                                        H         CH.sub.3 CH.sub.2                                                                      H                                        O      CH.sub.3   H         CH.sub.3 H                                        O      H          H         CH.sub.3 H                                        O      CH.sub.3   H         H        H                                        O      H          H         (CH.sub.3).sub.3 C                                                                     H                                        O      CH.sub.3 CH.sub.2                                                                        H         n-C.sub.4 H.sub.9                                                                      H                                        O      CH.sub.3   CH.sub.3 CH.sub.2                                                                       CH.sub.3 CH.sub.3 CH.sub.2                        ______________________________________                                    

When the tetrahydrothiophenes of the above formula are contacted with anequimolar amount of hydrogen peroxide or m-chloroperbenzic acid thecorresponding sulfoxide (X=SO) is formed in each case. Treatment of thesame starting material or the sulfoxide with a molar excess of the samereagents or potassium permanganate affords the corresponding sulfone(X=SO₂).

PREPARATION X 3-Amino-2,2,4,4-tetramethyltetrahydrofuran

A. 2,2,4,4-Tetramethyltetrahydrofuran-3-one

4-Bromo-1-hydroxy-2,2,4-trimethylpentan-3-one (prepared as described inPreparation W, Parts A and B) 25 g. (0.1 mole) was dissolved in 160 ml.of ethanol and a solution of 8 g. (0.2 mole) sodium hydroxide in 80 ml.of water was added. The resulting mixture was stirred at roomtemperature for 30 minutes, diluted with water, extracted with ethylether, the extracts washed with water, brine and dried over anhydrousmagnesium sulfate. The solvent was evaporated to afford 17.7 g. of2,2,4-trimethylpentan-1,4-diol as a colorless liquid which wasidentified by ¹ H-NMR. The diol was dissolved in 50 ml. of chloroform,1.5 ml. of concentrated sulfuric acid added dropwise. The mixture washeated at reflux for 3 hours, while distilling water/chloroformazeotrope from the mixture. After standing overnight at room temperaturethe reaction mixture was washed with water, the organic layer dried(MgSO₄) and solvent evaporated in vacuo to provide 13.9 g. of colorlessliquid. Distillation afforded 8.3 g. of the desired product, B.P.70°-72° (50 mm.), overall yield 58%.

B. The ketone obtained in Part A, 8.0 g. (0.056 mole), hydroxylaminehydrochloride, 8.0 g. (0.113 mole) and sodium acetate, 2.3 g. (0.113mole), were combined with 85 ml. of ethanol and the mixture heated atreflux for 48 hours. The resulting mixture was diluted with water,extracted with ethyl ether, the extracts washed with water, dried andevaporated to yield 9.0 g. of a mixture of syn- and anti-oximes,identified by its ¹ H-NMR spectrum.

The oxime obtained above, 1.3 g. (8.28 mmole) was dissolved in 70 ml. ofdry ethanol, 1.9 g. of sodium metal added and the mixture warmed toreflux and held at this temperature for 15 minutes. Heating wascontinued for two hours with addition of two more increments (1.9 g.each) of sodium. The reaction mixture was then diluted cautiously withwater, extracted with ethyl ether. The ether layer extracted with dilutehydrochloric acid, the aqueous phase made alkaline with sodium hydroxideand re-extracted with ether. The extracts were dried (MgSO₄) andevaporated to dryness and the residue distilled to obtain the desiredamine, B.P. 68°-69° C. (15 mm). After further purification byprecipitation of the hydrochloride salt from ethyl ether-methanol,basifying the salt and extracting again with ether 0.87 g. of amine of93% purity by gas chromatography (OV-1 column) was obtained.

We claim:
 1. A D-amino acid amide compound of the formula ##STR315##wherein R^(a) is CH₂ OH or CH₂ OCH₃, and R^(c) is ##STR316## where X₂ isS or SO₂ and a. when n₂ is zero and p₂ is zero or 1, R⁴¹ and R⁶¹ areeach methyl,b. when n₂ is 1 and p₂ is 1, R⁴¹ and R⁶¹ are each hydrogen.2. A compound according to claim 1, wherein R^(c) is ##STR317##
 3. Thecompound according to claim 2 wherein R^(a) is CH₂ OH.
 4. The compoundaccording to claim 2 wherein R^(a) is CH₂ OCH₃.
 5. A compound accordingto claim 1 wherein R^(c) is ##STR318##
 6. The compound according toclaim 5 wherein R^(a) is CH₂ OH.
 7. The compound according to claim 5wherein R^(a) is CH₂ OCH₃.
 8. A compound according to claim 1 whereinR^(c) is ##STR319##
 9. The compound according to claim 8 wherein X₂ is Sand R^(a) is CH₂ OH.
 10. The compound according to claim 8 wherein X₂ isSO₂ and R^(a) is CH₂ OH.
 11. A compound according to claim 1 whereinR^(c) is ##STR320##
 12. The compound according to claim 11 wherein R^(a)is CH₂ OH.
 13. A compound according to claim 1 wherein R^(c) is##STR321##
 14. The compound according to claim 13 wherein R^(a) is CH₂OH.